Couple of iMac 2012 questions

RAM is only user-upgradeable on the 27" 2012 iMac, the 21" 2012 iMac needs a teardown to upgrade RAM and HDD.

If Apple doesn't offer to upgrade the hard drive for a fee, then I'll be stuck with the original forever. I just don't think I have it in me to remove the screen from the case. This is why I got the Fusion drive. My iMac needs to last 5-7 years, so I'm just not gonna take the chance to open it myself.

The answer to both of those questions really depends upon your skill with a guitar pick.

Or if you are not gutsy enough to use the guitar prick you can always bring your Imac to an authorized repair center and have them do it... If either the ram of the HDD need to be replaced because of a failure there must be a way..

I went for the 1TB Fusion drive in my 27" iMac purely because I think it is the best value for money.
With regard to upgrading the hard drive at a later date, you might feel more comfortable with doing it a few years down the road? Plus there may be a business doing it. I would say someone could make a bit of dough if they were to offer upgrades to the 2012 iMac in a few years time. Going behind the screen sounds horrendous to me, especially with my lack of skill and experience in that type of thing.