Mix insulation between joists 040 and 035?

Hello,

I am about to complete the project of my deceased father. The 2nd floor (one-sided pitched roof) and the attic are to be fully developed. About half of the roof area is already insulated with "Die neue Rockwool Dämmkeil 040 120mm". Since 040 intermediate rafter insulation is now difficult to find, I am considering insulating the rest with 035 mineral wool. Are there any problems with that?

Roof structure as follows:

CURRENT
Roof covering
Batten
Counter batten
Roofing felt, sanded
20mm rough plank sheathing
160mm rafters with
- 40mm ventilation gap
- 120mm 040 Rockwool

DESIRED
as above, then
Vapor barrier sd 2.3
Batten 60mm with
- 60mm mineral wool 035
Gypsum board 12.5mm
Plaster

Addendum:

or does the whole thing also work without ventilation with a humidity-variable vapor retarder?

SOLL is fine. You can mix the WLGs without concern. If you still have leftovers from the roofing felt and know the sd value, you can calculate whether ventilation is necessary. It doesn't do any harm.