import re
texts = ["G1X-10.599Z12", "X9.4Y800", "Y70.190", "X18.3", "X25Z13"]
for s in texts:
print( re.sub(r"X([^A-Z]+)", r"X[\1+#1]", s) )
aW1wb3J0IHJlCnRleHRzID0gWyJHMVgtMTAuNTk5WjEyIiwgIlg5LjRZODAwIiwgIlk3MC4xOTAiLCAiWDE4LjMiLCAiWDI1WjEzIl0KZm9yIHMgaW4gdGV4dHM6CiAgcHJpbnQoIHJlLnN1YihyIlgoW15BLVpdKykiLCByIlhbXDErIzFdIiwgcykgKQo=