So i decided to mod Rebellion beta to satisfy my personal needs, as i am awfully impatient and curious. 

As i have no previous experience with modding Sins, if i exclude that modelling stuff for Babylon 5 mod, i ran into first throwback rigthaway. So i opened the GalaxyScenarioDef file with Win 7 Notepad, ready to rewrite some stuff, i succesfully did that, saved it, tried to ran the game and UH-OH, it wont work anymore    Run-time error.  So i take it, messing with these entity files is not just simple thing of changing stuff within Wordpad? Do i need some other app - like something from those Forge Tools -  to open the entities and edit and save them (so they do not break the game)?

After replacing the edited galaxy scenario file with the original one, which i luckily kept as back-up, the game works again just fine, so i take it as confirmation, that it was indeed me messing with the game files causing it.

Thanks