Well, maybe I'm wrong.Or maybe not. I'm probably a poor judge of what a new or casual user considers easy or hard.
Do you think most moderators have a throwaway test account alreadyThat was two of the first bits of advice I learned when I joined a moderator help group: 1) have a second owner for the group, even if it is yourself with a second Yahoo Account; 2) have an account that you control signed up as a member of the group, so you can see the group's features as a member does.
The first is just insurance against having your primary account closed or compromised, or otherwise becoming unavailable. If the backup owner is an account of your own and not used for much else it could be (temporarily) demoted to moderator with no extra privileges, then used for this purpose.
The second is part of learning how Yahoo Groups works, so that you can answer members' questions like "why can I see my email address? Does everyone see it?". A "member" account could be (temporarily) promoted to moderator with no extra privileges, then used for this purpose.
Now, do "most" moderators (or owners, specifically) do this? Strictly by the numbers I'd have to say "no", as there are vastly more Yahoo Groups in existence than there is combined membership in the moderator help groups. But of the group owners that might be considering moving to another service the odds are probably better - those are already the subset that are paying attention to their groups.
And that they wouldn't mind giving access to that account to someoneThe key there is what other things are tied to that account - do they use it for email correspondence, a high ranking in Answers, a stash of photos at Flickr? Other uses would rule out (in my mind) giving the account credentials to someone. But I wouldn't do those things in an account I'm using as a backup.
To alleviate the concern your instructions for the process could make some suggestions:
1) Use (or create) an account which isn't used with other Yahoo services.
2) Make the account a moderator of the group, but uncheck all of the moderator privilege boxes.
3) Change the password to the account before giving it to Groups.io, and make sure this temporary password isn't a password you've used elsewhere.
4) After the transfer completes, change the password to the account again.
So, in this scenario, the steps would be:Sounds good and simple to me.