[wot-Mike]

First of all, a vBulletin upgrade does NOT overwrite customized templates, but it might be wise to revert to the "original" after upgrading and re-applying your changes, if necessary. Not all templates are different from previous versions...

Second, what helped me in the past is to keep change logs. Instead of re-applying every single hack by going through every single installation instruction, one at a time, I put all the changes into one large file, and sorted the changes based on the vBulletin files. That way I can apply all the changes for all the hacks to every single file at once, and then move on to the next file. I was able to install 8 or 9 hacks at once within half an hour