Once characters characters enter my Faerun (defined as any of my D&D
games in Faerun), they face certain restrictions on their extraplanar
mobility in the multiverse. The characters truly remain those of the
player who created them (and can go where they want); this rule only
means that you'll need to consider the continuity and fantastical
reality of my Faerun when deciding to use your character in other
games. If you take your character and 'teleport' him to someone
else's Spelljammer game, level him up, and expect to bring him back to
my Faerun, you may be disappointed. If you would like to carbon copy
a character for another game, that's fine, (s)he's your character!
Just expect a lot of scrutiny.