Hi Mark,
The best thing to do before upgrading your own vBulletin forum is to setup a test site, and install the modifications and style on that.
Generally going from major release to major 3.6 to 3.7 templates require a lot of work to upgrade. Going from minor version to minor version, most the time they are unchanged/slight modifications ex: 3.7.1 to 3.7.2.
Most modifications will work with the latest version of vBulletin, however there is never any way to be sure, other than upgrading a test site to make sure first.
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