[squidsk]

Your best bet to to upgrade to vb3.8.9 and redo whatever changes you need to make your customized theme work properly, there should be relatively few of those since you're doing minor version upgrades and not a major version upgrades (i.e. 3.8.3 to 3.8.9 not 3.7.x. (or older) to 3.8.9). 3.8.3 is very outdated and there have been a number of security issues patches since 3.8.3 was released so running a version that old is a bad idea and certainly the relatively minor inconvenience of having to do some template modifications is far outweighed by having the most patched version 3.8.x possible.

You also don't want to have to do core file edits on your own as those are way more prone to errors than fixing templates.