Also, it's not really a matter of "which time to change". Time stamps are handled by the file system, at least that's how things should be. I very much doubt that an application has any way of influencing which of the three possible time values are changed when you tag a file.
(Unix doesn't even know the exact "create" date of a file, only something that could probably be the create date if the file hasn't been moved or renamed.)

The other issue is what you expect to see in the image viewer when it sorts pictures "by date". As there is no create date that magically attached to the file, the image viewer could try to interpret the EFIF information... which could fail or could be wrong. (Aunt Hilda got her cam on christmas eve, didn't bother to read the manual and change setting, simply shot photos the whole evening... all tagged with 1.1.2002)

I'm afraid there won't be a solution to this. The only reasonable thing to do is to offer as many settings as possible in the application that interprets the data (the image viewer in this case), but Nokia decided for Maemo 5 that options are bad. So wait until a thrid party image viewer is available.