I am not absolutely positive about leaving FTX Central where it is and installing scenery. My opinion, I always switch to NA when installing scenery that uses FTX North America scenery (Pacific Fjords) as the base scenery for add on scenery. If I'm installing OZ scenery I switch to Australia etc. Better safe than sorry in my mantra. Besides it takes less than a min. to switch.
There is no self installers with the RTMM scenery ya gotta do it by hand. If you install one RTMM scenery, switch to NA, install the one scenery per the instructions. Switch to Default, then back to North America, to recycle the scenery library once. Then look at the FSX scenery library, if your RTMM scenery is still at the top above FTX scenery entries then your good to go. If the recycle sets FTX above the RTMM scenery file then rerun the Insertion point utility and set it below the RTMM scenery and EZ1 library.
Different folks use different methods to install scenery. You could add all the RTMM scenery into one large folder, IE: Folder named Misty Moorings with a scenery sub folder in which you place all the various RTMM scenery. The problem with this method is that if you have a problem along the line everything is mixed up together.
On my installation I have a Master folder named Misty Moorings, I then add all the various RTMM scenery into this master folder IE: C:\Program Files\Microsoft Games\Microsoft Flight Simulator FSX\Addon Scenery\Misty Moorings\
Misty's Place. (example of the added scenery is in bold each different scenery would be have its own folder with the scenery sub folder)
Long I know but I can manipulate any given RTMM scenery file individually this way. At present I have 48 RTMM scenery folders and that does not include the Aircraft Carrier scenery. It is just not in a location you would ever find a Carrier Air group operating so I opted to not install that one.