I don't think it makes any sense to have a mix of de-rated and full-rated engines - it's not as though they operate anywhere where the extra thrust would give them more payload and hence revenue, that's why they are threatening to withdraw from certain airports.
Also it would be a logistical nightmare to keep track of the aircraft and engines in terms of operational and maintenance requirements.
No, as said before, while Ryanair can get airports to lengthen their runways to meet the requirements for the de-rated version and gain the benefits of lower costs, they are not going to do anything different.