How do I link slides in different keynote 6.5 presentations? I had to presentations in the earlier version of keynote that were linked with a hyperlinked object. That option isn't found in 6.5. I need the presentations separate as one of them is customized with many pictures for each show, while the other remains the same. Combining them creates a file that is too large and thus problematic.

The hyperlink disappeared when the two presentations were "upgraded" to 6.5 and now I'm kinda screwed by having to stop the show and have the whole audience watch while I switch to the other presentation. Very unprofessional.
Unfortunately, Apple removed that feature (along with many others) when they released Keynote 6.  It's unclear why, but some people attribute it to a security concern?  Not sure if they ever intend to reinstate it.

Your best bet is to downgrade back, if possible.  I think the last version that had that feature was 5.3.