I have done something akin to that partial disassembly procedure on old rangefinder film cameras (exactly for the same reason - to clean the dust out of viewfinder) but never worked on modern electronic cameras. If You take a look at step 12 you will realize one flex connecting main controls on the camera back ... it could be easily damaged making your back camera controls pretty unresponsive ... even some of them ... for me this is a game stopper ;-)

That should be possible! Based on posted pictures it seems to me that top plate is being hold in place by 5 points. Two of them are easily accessible from the front (step 19) but other 3 are hidden and may require partial disassembly to get proper access. There is one screw on each side of a camera (step 9 on top and step 14 n top) but most difficult is the one hidden behind back panel (step 13 red circle) to get there may really require taking the whole back of the camera off. Unless You are skilled with some level of previous experience .... I would let the technician to clean the dust out.