I have registers instantiated in a Register block
//Here an attempt to do bit flips
bitFlipLocation = $random;
force DUT.RegBlock.Register1.reg[bitFlipLocation] = ~DUT.RegBlock.Register1.reg[bitFlipLocation];
DUT.Regblock.Register1, RegisterA, RegisterABC, ...
There are ways to do this, but not within the SystemVerilog language itself. You can write VPI code in C to iterate over block names and apply the forces use the C API. Or you can use tool specific commands to iterate of block names and use commands (usually Tcl) to apply the forces.
Both of those are beyond the scope of what can be shown in this forum.