Why would Wigan Warriors agree to a revised rental agreement when their current agreement (which is an immensely good deal in their favour) is contractually binding? For example, let's say I signed a 50 year binding contract with the owner of a top of the range Ferrari giving me the right to drive that Ferrari twice a week for the price of £10 a month where only I and not the current owner or any new owner of the Ferrari down the line have the ability to break that clause. Then, 20 years down the line the owner sells the Ferrari to someone else, who then contacts me, telling me that the price has gone up to £100 a month, I'd wave the contract in their face and tell them to fuck off.
This essentially is what Ian Lenegan can do (and probably has done) to the Spanish should (as many suspect) they be looking to increase their rent.
Whelan's fucked us over on that deal and there's nothing we can do about it until 2050 or whenever the deal ends. Unless of course, the Warriors turn Robin Park into their own ground and leave the DW permanently.