I have two groups and one group has a soldier, and an ASL, (now SL from SL being killed), only in it. Can this SL individual transfer to the other group?
SL or ASL doesn't matter for individual transfer--either can initiate a transfer to or from his group.
I'm not reading anything against or for it. I know one of the groups needs an SL or ASL in them, but doesn't mention if this commander can actually transfer himself.
Yes so long as he is unpinned and not an infiltrator (or enciecled or in a minefield)--an SL/ASL (since he himself is in the group that is being transferred from) can initiate a transfer of himself.