If I change to the One Rate, do I have to check the installation or change the measurement equipment?
Changing to a different company does not involve any change to your installation or interruption to supply. You don't have to do a thing: Endesa will take care of all of the paperwork.
Remember that:
Right now, all companies are replacing meters with new electronic models. If yours hasn't been changed yet it will be changed soon, but this has nothing to do with signing up for this rate.
If when signing up for this rate you decide to change the power or the time restriction rate for your rate, modifications must be made to your meter or ICP. This has a cost known as "coupling rights" which comes to €9.04 without taxes (Order ITC/3519/2009) If you increase capacity there may also be other contracting costs.