To update the extended offsets... Yes, you can. The same way you're doing the G54s. Only G54.1 starts at #7001 and goes:
1st axis 2nd axis 3rd axis 4th axis 5th axis 6th axis
G54.1 P1 #7001 #7002 #7003 #7004 #7005 #7006
G54.1 P2 #7021 #7022 #7023 #7024 #7025 #7026
G54.1 P3 #7041 #7042 #7043 #7044 #7045 #7046
.
.
.
G54.1 P48 #7941 #7942 #7943 #7944 #7945 #7946
And no, you can't rewrite G10 in the program. But, thats why you're probing. Just use the G10 for a "basic".... fine tune by probing.
Now, if you're creative, you can use variables in your G10 instead. Then everytime your probe runs, you're updating the "programmed" G10 so to speak. Don't think its worth doing that though. Just probe it....
It's just a part..... cutter still goes round and round....