How to upgrade ECC with ChaRM in place?

Dear experts,

Context

• I have to upgrade a landscape from ECC 6.0 Ehp4 to Ehp7.  (Dev->Qa->PreProd->Prod).
• We have ChaRM in place (with solman 7.1 SP10).

Questions

• For Dual Maintenance, Is it possible (or how to) use charm  for both the Main and the Parallel landscape? (Given ChaRM does not accept 2 dev environments at the same time).
• If the above is possible, any special consideration to use retrofitting?

Thanks in advance.

Mariano Billinghurst.