Reg thin pool and discard handling

Hi Team,
A very happy new year to you all.

When a thin pool is created it has option to control discard behavior.
Typically the useful ones are either discard_passdown vs no_discard_passdown.

My question is as below:
If the thin pool is in "no_discard_passdown" and later changes to
"discard_passdown", would there be a way to reinitiate discard for
those ranges that was not passed down?

Typically fs sitting on top of the thin lv controls discard ranges and
that was already handled as "no_discard_passdown".
Later if say, the backing storage gets filled up, then how can one
re-initiate discard again to allow it to reach
backing storage?

Thanks for your pointers.

Best regards