The back shell isn't really involved in heat dissipation per se. Most of the heat is carried by convection out the vent. The critical thing is that the back cov

The back shell isn't really involved in heat dissipation per se. Most of the heat is carried by convection out the vent. The critical thing is that the back cover is carefully engineered, in coordination with the spacing to various bits of the internals, to selectively restrict airflow, to produce the needed flow patterns to cool all the internals. But, yes: if you change the inner mould line there's the risk of some components not getting the airflow they need. It might not even be obvious, as not everything has a temperature sensor.