Is it possible to mod the steam version of Fallout New Vegas

Sure it is possible. you are limited to mods that Do Not require nvse only in case you are playing the german no-gore Version. Anyway mods can be found on vegasnexus for example. Copy them to c:/programs(x86)/steam/steamapps/Common/newvegas/data and activate them in the launcher. For details refer to included readmes.