One step at a time

There should be a firmware for 5i25/ 7i76 that has BOB on one of the headers, but not sure there is for 7i76E, so check the downloaded zip file from Mesanet.com.
Or wire manualy 7i76e outputs to a DB25 connector, so no firmware flashing required.

Since you own a G540 i would like to assume you also own a DB25 cable that goes from it to the PC, soooo cut that cable, find what wire goes where on the G540 and bolt it down to where it belongs on the 7i76E.

If you go the "cut the cord" route, you just do a normal config using pncconf and you're done. No flashing required.

The other option needs
-new firmware (=bothering PCW)
-flashing that firmware
- a 26 pin header to DB25 cable, chance are you have to order that and wait for it
- before all that, decide where should the first 4 stepgens be and let PCW know about it, more info
stepgens or step generators are hard wired on Mesa boards so when LinuxCNC loads say 3 stepgens those will always be stepgen 0, stepgen 1, and stepgen 2. Also those stepgens will be connected to output pins that can not be changed .
Now in your case you already have 5 stepgens on 5 pairs of pins on the 7i76E terminals, so with new firmware it can be set to have 4 more stepgens on one of the 26 pin headers ( or more on the other header ), so if the new 4 stepgens are AFTER the 5 existing ones, it would need to have 9 stepgens loaded in hal and set to use stepgens 5,6,7,8 also in hal.
Or it can be set to have the 4 stepgens on the header as 0,1,2,3 and the existing ones on the board as 4,5,6,7,8.
Suddenly sacrificing a DB25 cable seems easier.