i think i already know the answer, but i thought i'd ask anyway.....

i bought a yearly pass a couple of months ago to Yosemite, but my question is... are you able to "upgrade" and pay for an all National Parks yearly pass? or is it too bad once you purchase the Yosemite one only?

I recall a few years ago I just paid for the one-week entry and they told me had I like 2 weeks to upgrade to the yearly parks pass. Don't know what the answer is for upgrading from a Yos only pass to the full one.

I did this over the summer in 2016. We purchased a Yosemite yearly pass at the park. A couple of months later I was able to upgrade the pass at Pinnacles NP for the cost difference. Note, they don't reset the date. The expiration date will stay the same as the original purchase date. So in this case I purchased a yearly Yosemite in July 2016. In October I upgrade to a NP yearly at Pinnacles NP, the new yearly NP pass has a July 2017 expiration date.

Hope this helps.

Chris