Towards the end of 2014 Engine development became a big issue with Ferrari and Renault trying to get the engine freeze lifted in order to close the gap on Mercedes.
But poor wording in the technical regulations has opened the door for teams to make changes to their 2014 engines.
An FIA spokesman told Autosport: "It was always envisaged, although not explicitly stated in the rules, that manufacturers would have to deal with modifications on the engine within the constraints of the rules, and then submit their 2015 engine [at the first race].
"It is simple, but when you read it [the rule book], it doesn't say that unfortunately."
F1's engine freeze
Current rules state a certain amount of development can be undertaken on engines year-on-year, with manufacturers able to change 48% of 45 engine components at the end of the current campaign.
But changes are only allowed to take place out of season and will be scaled down from 2015 onwards. This season engines were homologated on February 28, after which point changes were only allowed for reliability, safety or cost saving reasons.
As a result of that homologation, Renault and Ferrari have spent much of 2014 on the back foot and unable to cut the advantage enjoyed by Mercedes power.