I doubt that... because converting yourself to a general backpacking permit logically means that you've terminated your thru hiker status... yet didn't end that hike 50 miles beyond the park.
I think bottom line, the park service is being extremely flexible towards thru hikers (compared to general backpackers) and simply subjects them to a couple of simple rules. One of these rules is the 8 day limit.
If your plans deviate from what the thru hiker permit allows, then your only other legal choice is general backpacker permits.