Swarming and depleting ammunitions of airdefense is the only way I can see them flying and useful as a UAV. A one way ticket to enemy airspace and turning in circle until fuel depleted...
Refitting those old jets like the cheap expendable target drones, they will be going oneway. No weapon nor bombs nor missiles to be carried only full tank of fuel.
Their only mission is to get shot down by enemy air defence missiles in order to deplet enemy's stock of SAM, like what the Israelis did to Egypt air defence during the 1973 war, with decoy drones depleting Egypt's frontline SAM inventory along the Suez cannal.
If they are not shot down, just crash them at enemy air base or navy base, with ignition of fuel to do the damage.
Even if the modification cost is high, above $millions as some suggest, a few hundred million dollars expenditure with no human life lost is worth it, even if $billions are spent for successful unification of a rebel province, it is still worth it.