They already did a static fire with the new deluge system and it seems to work just fine.

The FAA has continued to trust SpaceX and issue licenses as they address issues. Keep in mind the FAA issues launch licenses for each of the hundreds of Falcon 9s they've launched so far, has issued more launch licenses for them than for any other company ever, and has a long working relationship at this point.

Iterative design isn't really a problem and we wouldn't have reusable rockets at this point without it.