Just read through the post, and you seem to have been taken around the houses a little! I'll give you a quick guide on resizing a SnapMirror destination.
To resize your destination volume
1) Quiesce the SnapMirror destination (command line: "snapmirror quiesce vol_name")
2) Break the SnapMirror relationship (command line: "snapmirror break vol_name")
3) Disable Fixed FS Size (command line: "vol options vol_name fs_size_fixed off")
4) Grow the volume (command line: "vol size vol_name +size_to_grow")
5) resync the snapmirror (command line: "snapmirror resync vol_name")
Don't re-initialize (that'll re-baseline it!), and don't worry about A-SIS settings. Once a volume has been SnapMirrored, you shouldn't need to restrict it again, this is only for re-initializing (which you shouldn't need to do).
This whole thing can be a little tedious and quickly gets a bit annoying if you grow your volumes regularly. Can I recommend that you thin provision your SnapMirror destination volumes? Set the volume size to the maximum space you have in your aggregate, but set the space guarantee to "none". Then when you do a SnapMirror initialize (or indeed resync it if it already exists), this setting is over-written and the size is fixed (fs_size_fixed) using SnapMirror. As the source volume grows, the destination will also grow.
The only thing you have to watch out for here is if you have more space on your source than your destination, you could end up filling up the destination entirely, so just keep an eye on that.