No, the titled owner is the owner, the lienholder merely possesses a lien. The vehicle legally belongs to the owner, not the lender. While the lender does have some contractual rights, they are not the owner. You don't have to consult with them before modifying your vehicle.Technically....unless you paid cash and the title is in your name with no lien on it, that's not true. Until you pay it off, the vehicle legally belongs to whoever gave you the loan.
The could easily include language in the contract requiring the lock out and allowing use if you miss "X" payents as part of the terms; and most people would be happy to sign it. In which case, removing the antenna, or defeating it in any way, would be breach of contract.