I know it's the middle of June but was the 8GB update merely timebomed on the download? I guess what I am asking is could you simply give someone who buys the 8GB, today, the file and they'd be able to update their version with golf support?
If you want the device to act and feel completely stock, but have the current golf and keep up to date, I think you might need to flash an old community-sourced ROM based off a slightly out-of-date official package, and then use the bundled Motorola software to update to the latest version.
They work some fancy magic where you never even have an actual file, and all downloading/updating/flashing happens through the MotoActv software you install on your PC.
But as long as you have the Golf features active, all future updates will keep those features there for you - but if you were to never have had Golf, the current software won't enable it (to the best of my knowledge).
I'm fairly certain, of what I have read from the official topic on XDA, that if you update through the official channels over a custom ROM, it'll work but just overwrite the custom aspects.
I still haven't rooted my motoactv, but I might be doing that soon. It's gotten to be what seems like a painless process and things are pretty ironed out - they basically just give you the official ROM but open it up wide to allow typical Android customization.
http://forum.xda-developers.com/showthread.php?t=1399692
(a very lengthy thread - I'd probably start around page 160, read forward from that and then read backward from there. You should get the gist of the latest tips and tricks (if comfortable doing this).
There might be official packages out there used for "recovery" purposes in case of a brick. Which you'd need the Software Update 6.6 (MA 1.6.6) to enable the Golf features, and once enabled, they'll remain there after every update (and even improve, perhaps - not sure if the 8GB has had golf feature improvements, but they have improved it for the 16GB at a minimum).
The discussions in that XDA topic, coupled with the information and instructions at the wiki page below, should set you up for success.
http://motoactv.wikispaces.com/