Will I get charged for having my meter changed?

I've just moved into a new property which has a single rate electricity meter but I want to be on economy 7. I also want to change to a different supplier than the one the previous tenants were using.

The energy supplier I want to go with said they will have to charge me £80 to change the meter to an E7 one. So I thought, what if I get the existing energy supplier to change it to E7 just before I leave. I rang them up and created an account in my name. I've gone onto their standard variable rate tariff (so no exit fee or tie in period). I was told I can then request (with fee) a E7 meter which would then allow me to go on their normal E7 variable rate tariff (also without exit fee and no tie in).

I thought that once I had done that, there was nothing to stop me from leaving them and going with the energy supplier I wanted to go with.

Is there any issue with this? Is there some implicit tie in period due to a meter change? I did ask them and they didn't say there was but I've been in situations before where things were missold.