Attached the shell scripts using awk and sed how I have migrated two separated logbooks into one single and how I re-adjusted certain attributes.

#!/bin/bash
# KR84, 28.10.2019

# the input files are the exported XML files from ELOG -> Finden


# search in XML for sring between <DATE> and </DATE>
# and replace with: <DATE> and </DATE><When> and </When>
echo "converting export_rf.xml ..."
cat ./export_rf.xml | 
    sed 's/<Personnel\(.*\)Personnel>/<Author\1Author>/g' |
    sed 's/<DATE\(.*\)DATE>/<DATE\1DATE>\n\t\t<When\1When>/g'   |
    sed 's/<Subject>\(.*\)<\/Subject>/<Title>\1<\/Title><Entry_Type><\/Entry_Type>/g' |
    sed '/<Machine>SwissFEL<\/Machine>/ {N;N; s/<Machine>SwissFEL<\/Machine>.*<Domain>OBLA<\/Domain>.*<Section>TRFCB/<Machine>OBLA<\/Machine>\n\t\t<Domain>All<\/Domain>\n\t\t<Section>TRFCB/g}'  |
    sed 's/<When>Mon, /<When>/g'                          |
    sed 's/<When>Tue, /<When>/g'                          |
    sed 's/<When>Wed, /<When>/g'                          |
    sed 's/<When>Thu, /<When>/g'                          |
    sed 's/<When>Fri, /<When>/g'                          |
    sed 's/<When>Sat, /<When>/g'                          |
    sed 's/<When>Sun, /<When>/g'                          |
    sed '/<When>.*<\/When>/{s/ Jan 20/.01./g}'                    |
    sed '/<When>.*<\/When>/{s/ Feb 20/.02./g}'                    |
    sed '/<When>.*<\/When>/{s/ Mar 20/.03./g}'                    |
    sed '/<When>.*<\/When>/{s/ Apr 20/.04./g}'                    |
    sed '/<When>.*<\/When>/{s/ May 20/.05./g}'                    |
    sed '/<When>.*<\/When>/{s/ Jun 20/.06./g}'                    |
    sed '/<When>.*<\/When>/{s/ Jul 20/.07./g}'                    |
    sed '/<When>.*<\/When>/{s/ Aug 20/.08./g}'                    |
    sed '/<When>.*<\/When>/{s/ Sep 20/.09./g}'                    |
    sed '/<When>.*<\/When>/{s/ Oct 20/.10./g}'                    |
    sed '/<When>.*<\/When>/{s/ Nov 20/.11./g}'                    |
    sed '/<When>.*<\/When>/{s/ Dec 20/.12./g}'                    |
    sed 's/ +0100<\/When>/<\/When>/g'                                     |
    sed 's/ +0200<\/When>/<\/When>/g'                                     > export_rf_modified.xml



#    sed 's/ Jan 20/.01./g'                              |
#    sed 's/ Feb 20/.02./g'                              |
#    sed 's/ Mar 20/.03./g'                              |
#    sed 's/ Apr 20/.04./g'                              |
#    sed 's/ May 20/.05./g'                              |
#    sed 's/ Jun 20/.06./g'                              |
#    sed 's/ Jul 20/.07./g'                              |
#    sed 's/ Aug 20/.08./g'                              |
#    sed 's/ Sep 20/.09./g'                              |
#    sed 's/ Oct 20/.10./g'                              |
#    sed 's/ Nov 20/.11./g'                              |
#    sed 's/ Dec 20/.12./g'                              |




# search in XML and add offset to all IDs because they shall not overlap when merged.
echo "converting export_llrf.xml ..."
cat ./export_llrf.xml           | sed 's/<Subject>\(.*\)<\/Subject>/<Entry_Type><\/Entry_Type>\n\t\t<Status><\/Status>\n\t\t<Title>\1<\/Title>\n\t\t<Inv_ID><\/Inv_ID>/g' > export_llrf_modified1.xml
cat ./export_llrf_modified1.xml | awk -F'\t\t<MID>|</MID>||' '{ if ($2!="") {print "\t\t<MID>"$2+2016"</MID>"} else { print $1} }' > export_llrf_modified2.xml
cat ./export_llrf_modified2.xml | awk -F'\t\t<REPLY_TO>|</REPLY_TO>||' '{ if ($2!="") {print "\t\t<REPLY_TO>"$2+2016"</REPLY_TO>"} else { print $1} }' > export_llrf_modified3.xml
cat ./export_llrf_modified3.xml | awk -F'\t\t<IN_REPLY_TO>|</IN_REPLY_TO>||' '{ if ($2!="") {print "\t\t<IN_REPLY_TO>"$2+2016"</IN_REPLY_TO>"} else { print $1} }' > export_llrf_modified.xml

rm -rf ./export_llrf_modified1.xml ./export_llrf_modified2.xml ./export_llrf_modified3.xml 

cat ./export_llrf_modified.xml | 
    sed '/<Machine>SwissFEL<\/Machine>/ {N;N; s/<Machine>SwissFEL<\/Machine>.*<Domain>Test Systems<\/Domain>.*<Section>TRFCB/<Machine>OBLA<\/Machine>\n\t\t<Domain>All<\/Domain>\n\t\t<Section>TRFCB/g}'  |
    sed 's/<When>Mon /<When>/g'                           |
    sed 's/<When>Tue /<When>/g'                           |
    sed 's/<When>Wed /<When>/g'                           |
    sed 's/<When>Thu /<When>/g'                           |
    sed 's/<When>Fri /<When>/g'                           |
    sed 's/<When>Sat /<When>/g'                           |
    sed 's/<When>Sun /<When>/g'                           |
    sed 's/-Jan-/.01./g'                              |
    sed 's/-Feb-/.02./g'                              |
    sed 's/-Mar-/.03./g'                              |
    sed 's/-Apr-/.04./g'                              |
    sed 's/-May-/.05./g'                              |
    sed 's/-Jun-/.06./g'                              |
    sed 's/-Jul-/.07./g'                              |
    sed 's/-Aug-/.08./g'                              |
    sed 's/-Sep-/.09./g'                              |
    sed 's/-Oct-/.10./g'                              |
    sed 's/-Nov-/.11./g'                              |
    sed 's/-Dec-/.12./g'                              |
    sed 's/ +0100<\/When>//g'                                     |
    sed 's/ +0200<\/When>//g'                                     |
    sed 's/<\/When>/:00<\/When>/g'                      |
    sed 's/<When>-:00<\/When>/<When><\/When>/g'                    > export_llrf_modified_datetime.xml

echo "export_llrf_modified_datetime.xml need manual edit for empty <When></When>"

#!/bin/bash
# KR84, 28.10.2019

# generate emtpy auto-fwd text for LLRF for 3100 entries and offset of 2000
echo "generated import_llrf_fwd.xml"
echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" > import_llrf_fwd.xml
echo "<ELOG_LIST>" >> import_llrf_fwd.xml

declare -i ID
declare -i IDNEW

for ID in {1..3013}
do
    IDNEW=$ID+2016

    echo -e "\t<ENTRY>" >> import_llrf_fwd.xml
    echo -e "\t\t<MID>${ID}</MID>" >> import_llrf_fwd.xml
    echo -e "\t\t<DATE>Mon, 28 Oct 2019 20:00:00 +0200</DATE>" >> import_llrf_fwd.xml
#    echo -e "\t\t<DATE>28.10.2019 20:00:00</DATE>" >> import_llrf_fwd.xml
    echo -e "\t\t<ATTACHMENT></ATTACHMENT>" >> import_llrf_fwd.xml
    echo -e "\t\t<ENCODING>HTML</ENCODING>" >> import_llrf_fwd.xml
    echo -e "\t\t<When>28.10.2019 20:00:00</When>" >> import_llrf_fwd.xml
#    echo -e "\t\t<When>1572289200</When>" >> import_llrf_fwd.xml
    echo -e "\t\t<Author>Kalt Roger (KR84)</Author>" >> import_llrf_fwd.xml
    echo -e "\t\t<Machine>SwissFEL</Machine>" >> import_llrf_fwd.xml
    echo -e "\t\t<Domain></Domain>" >> import_llrf_fwd.xml
    echo -e "\t\t<Section></Section>" >> import_llrf_fwd.xml
    echo -e "\t\t<System></System>" >> import_llrf_fwd.xml
    echo -e "\t\t<Subsystem></Subsystem>" >> import_llrf_fwd.xml
    echo -e "\t\t<Subject>Automatic forward</Subject>" >> import_llrf_fwd.xml
    echo -e "\t\t<TEXT>&lt;meta http-equiv=&quot;refresh&quot; content=&quot;0; URL=&apos;https://elog-gfa.psi.ch/SwissFEL+RF/${IDNEW}&apos;&quot; /&gt;</TEXT>" >> import_llrf_fwd.xml
    echo -e "\t</ENTRY>" >> import_llrf_fwd.xml
done

echo "</ELOG_LIST>" >> import_llrf_fwd.xml