Just back from doing what you said Scott.
I replaced the mph by km/h afraid that I might ruin the brake shoes when using the handbrake for too long or at a too high speed.
No e-brake button here, it's a E53 built in 2003 (218PS).
Handbrake is as effective now as it used to be
Pretty sure the coating is gone now.
Yes I did clean all the brake discs with brake cleaner before installing them just in case they would have an oil-based coating as well.
Cleaned them after installing them again.
Just read on THIS page (the manufacturer of my brakes and pads) that they "can be fitted directly without cleaning or additional treatment".
Although they also say that "the coating does not lead to any significant reduction in the friction coefficient" I feel a much better deceleration now compared to yesterday.

I am a high speed freeway flyer often doing 120mph (legal on most roads I'm driving).
Had to replace the discs due to excessive rust on it...
No idea what kind of pads I have.
According to the manufacturer: "ensures full braking performance from the very beginning".

Thanks all