In reply to chr_sue:
‘force’ is an action which questa supports, which places/drives a value onto a signal/net/reg inside the design.
That value can either be ‘frozen’ - left there forever so that the signal/net/reg will not change value, no matter what - or can be ‘deposited’ - set once, and after that the value might be changed by the DUT, for example when the reg is written to thru a processor interface in the normal way.
A backdoor access to a reg would typically not be a ‘freeze’, since backdoors are used primarily for initial setup of a DUT, or for some very specific register access testing.
HTH