You do not have to own any expansions to do tradeskills. Tradeskills are not tied to zone access and level caps. (With exceptions, see below)
You may be limited in what supplies you can get and tradeskill quests you can do because you can't go to certain zones and you may be limited in some of the recipes you can acquire if your level cap is 50. (Recipes as in Enchanter transmute spells, etc)
In short, yes you can do the new research as soon as the research code goes in and you do not have to buy the new expansion at all. (Unless of course they put ingredients only in expansion zones and make them NO TRADE)
Edited, Oct 8th 2008 5:32am by Reyla
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After 16 years, I'm not listing every friggin character.