If you are asking if the FSDT installers supports FSX:Steam, they surely do. Just be careful to reinstall using the proper procedure, which is:
- Uninstall all your add-ons from FSX, at least those that have an uninstaller. Do this first.
- Uninstall FSX using its own uninstaller. DO NOT remove its folder manually, this will left its registry keys and will completely mess up the following FSX:Steam install. A Windows restart might help after this step.
- If you are absolutely sure you uninstalled the original FSX using the standard uninstaller, you can finally remove the old FSX folder, which will now likely contains add-ons that didn't have an uninstaller ( those that did, should have gone after the first step ).
- Install FSX:Steam. DO NOT INSTALL ANY ADD-ON just yet.
- RUN FSX:Steam once. This is REQUIRED, so at the first install, the Steam software will create all the proper registry keys for FSX:Steam, which should now configured to run in "Single FSX mode" ( without the original FSX installed alongside with it ), without this step, add-ons installers will surely fail.
- NOW you can finally reinstall all your add-ons.