I just do it the old fashioned way and untick them in the scenery library instead of using an external editor. For me its just as simple
Same here. No need for any extra software to do it.
Even though many simmers keep writing disabling other sceneries does not influence VAS, my experience is different.
Plus if I one uses a lot of addon scenery, it should be remembered that sometimes there will be some extra problems with some of them.
I mean not only high VAS usage due to using photoscenery, but also some problematic textures or bgls (e.g. AFCAD files), which the user may not be aware of.
Disabling them takes most of these problems away. So my experience is that it is always smart to keep only e few sceneries active.
I used to check VAS usage regularly (now I rarely do it) and have seen noticeable differences with different numbers of sceneries active. Up to 1 GB!
For instance at the very moment I have 51 airports installed, almost exclusively in Europe (except for Yekaterinburg and Dubai).
But less than 20 are currently active in my scenery library, just those I mostly fly and those I am currently flying from/to.
Once I notice any memory problems (none right now), I will not hesitate to reduce this number further.
One more remark is I am not sure any external scenery managers are actually able to deal with full deactivation of airports.
The reason is some files are installed in different folders, for instance AFCAD, altitude and terrain bgls (but not only).
An example may be Aerosoft's Afd folder where some German airport files go, or the FSX Scenery\World\Scenery folder, which ususally collects quite a lot of new bgls.
Plus there are some scenery installers (hate them of course) which will replace some stock FSX bgls with new ones.
All in all, there is no perfect solution in the search for getting some relief to FSX, but I add my voice to deactivating unused scenery.