Is this possible with tortoiseSVN?:
Always freeze svn:externals
for tags
the scenario is our trunk will always use the \'HEAD\' revision for externa
I know this isn't for tortoiseSVN, but if you use eclipse with subversive, you can right click the project and select team->tag. Subversive freezes externals by default and formats the properties quite nicely.
You can try svncopy.pl (find it on google) It is a perl script that answer your need.