IMO (worth about $.02), No, do not change how your thumbs are base on how your arms are.
I use the same grip for revolvers, semi-autos, single shots.
Thumbs forward and no finger on the front of the trigger guard.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)