Users editing *just* prefixes, not the whole post in forsale forum. How?

[goldoff]

Hello,

I have been searching for this, but it seems either it hasn't been asked or I just I cannot find it...

I have a sales corner where I put the usual prefixes: ForSale, WantToTrade, WantToBuy... and another pack (of prefixes) about finished actions: Sold, Traded, Found...

By (my) default users cannot edit ads to prevent altering info (from description to price of the item sold/traded), so there is a lot of work for the moderators changing the prefixes once items are sold, etc while it should be the users' duty...

And here comes my question:
Is there any hack which allow users to edit prefixes but *only* prefixes?

or

is this technically possible?

Thanks for reading :)