Thanks for your reply. Does this mean I can use an Estab file, that came for example as part of an Eastern Front scenario, with another user created West Front scenario?
Unless you're talking about altering the scenario data with the SceneMaker routine, no, and even then, there's no guarantee it will work.
The Estab file is set up sequentially with each entry delineated by a unique designator. If the designator for say, an British Infantry Company in the original scenario's Estab file, matches the designator for an SS Armored Regiment HQ in the file you use in the altered scenario, all the units which should be infantry will become Armored Regiment HQ units in the altered scenario. This assumes, as Bie mentions, that the equipment designations transition from one Estab to another. Those are set up sequentially as well.
Unless you're designing your own scenario, it's best not to alter the Estabs for the scenarios already available.
Developers don't mind if you build off of the standard Estabs that come with the commercially available scenarios. But common courtesy and sound software development discipline should be one's guide for providing an alternate name of the altered Estab as a courtesy to both the original developers and fellow game owners who may inadvertently overwrite a standard Estab with a speculative one developed by someone using the editor.
There had been some talk about copy protecting maps, scenarios, and Estabs for the commercially released games. I'm not certain if that has been implemented.