If a hardwired interconnect to the grid is what triggers your permit/license requirements, then forget that I threw out the "backup" functionality. Ignore the grid connection and just treat the monthly service charge as another tax.
Or if you can get away with having a power inlet on your off grid system and powering that system from the grid with an extension cord during temporary backup/maintenance conditions only, go for that.
For my own AHJ, grid interconnect has nothing to do with whether permits/licenses are required (and for homeowner work, they're not). So an off-grid system and grid-connected are under the same requirements there regardless. A grid-tie system that can feed back power to the grid requires additional signoff/agreement with the POCO though.
(I'm very sympathetic to the situations where the utility will demand some stiff fee to build out a grid connection to a new residence, while local regulations require this connection for occupancy. But this isn't what you described)
