As long as we don't modify our F-16s or tinker with it in any way and we don't use it as an aggressive first strike platform against India inside Indian territory ... then we don't violet any agreement with the US govt.
Whether the US would sell us a Tanker? Not likely. But if we can modify some existing tanker, the US may not like it ... but cannot stop us.
Probably we have not done it already because it costs a lot of money to do these things and we already have to pay for ...
1. Building new Thunders
2. Acquiring/Building new Submarines from China
3. Acquiring/Building new Frigates From China
4. Building new Tanks
5. Acquiring Gunships
6. Acquiring plethora of support platforms and vehicles for the Army, Air Force and the Navy
7. New munitions
8. Maintenance & Operational costs of existing equipment (for all three services)
9. Upkeep and Expansion of our strategic and Unconventional Arsenal
etc. etc.
We have enough on our plates at the moment to pay for IMHO. But the Il-78P Midas AAR platforms are there for the air borne replenishment for our Thunders and Mirages. So maybe F-16 specific AARs, under current circumstances, may not be in high in priority.