Unrelated
For external_libs
repo I'll suggest to use inverted hierarchy
/(trunk|branches|tags)/(lib1|lib2|...|libN)
Short answer
Yes, keeping history of changes in lib*
in new repository is possible
Longer answer
You can move data and all related revisions of \ libraries\lib*
into new repository, but it will require to use tools outside of TortoiseSVN. Namely: you must to create dump of repository-part (svnadmin dump ...| svndumpfilter ...
or just svnrdump dump URL
) and loading this dump (svnadmin load --ignore-uuid --parent-dir ...
) into new repository. After load you have to change all externals definition in project1