Hi @chantal_diva arts,
It seems to be difficult, because you have much more invinsible character than only the xml markers in your document.
I think one good way could be @obi-wan Kenobis way.
Perhaps you can upload an example idml on a file hoster of your choise (e.g. xup.in).
Regardless, you can try the following:
1. text search:
<FEFF>
replace with:
##
2. grep search:
(?<=\b##)(.)
replace with:
\r$1
3. clean document
grep search:
#+
replace with:
(nothing) an empty replace field
Have fun