Isolator switch for electric generator to change from bonded to floating neutral
The root problem is you are modifying an appliance that is UL-listed, thus, voiding the UL listing.  And further, you create a situation that Code really does not like, where a procedure is essential to safety.  Code wants interlocks to be mechanical.
Assuming this thing has an internal GFCI to keep you honest, the problem is on the other side: when you've disconnected it from the house and are now using it portable, and you forget to restore the N-G connection.   Again the internal GFCI will protect you here, if it exists and works - but not every outlet has GFCI.  In fact the company has a page on how to disconnect the N-G bond for powering a refrigerator (which often trip GFCIs).
I am a huge fan of &quot;permanent wiring done temporarily&quot;, so I would just bolt on a small box and put the appropriate wrenches in that box, and simply follow the factory procedure for removing/reapplying the N-G bond.
If you had to use a switch, I agree, a 12V switch is probably insufficient. Your best bet that's readily available is 30A snap switches intended for water heaters etc.  If it's 2-pole, parallel it. (still a codevio, but more suitable for the service).