Flash-cells can be used as downcounters - ?

You can sort of count down FF, 7F, 3F, 1F, 0F, 07, 03, 01, 00

Those particular Spansion Flashes can be reprogrammed on a word (not byte) basis. Some other Spansion series have significant limitations on the number of times you can reprogram bytes or words and indeed which combinations of bytes/words can be reprogrammed "Programming to the same word address multiple times without intervening erases (incremental bit programming) requires a modified programming method. For such application requirements, please contact your local Spansion representative."

You must not even try to write a 0 bit back to a 1 bit, always rewrite the 0 to 0, otherwise you will get errors due to the illegal operation. These errors may cut the operation short before the programming of the desired 0 is fully complete.

Remember Flash is an analog device.

Cheers, Alf