the conclusion we can to last time was the wargear list says you can "exchange one or more items for an item from one of the Space Marine wargear lists" (emphasis is mine), meaning you get a single item from the list for each item you exchange
The reason I used the tag was mostly because at the time I originally did custodes (which was the first to use that tagging system) Bscribe really, really didn't like validation being done that way on lists if they were nested inside other lists (like weapons)
if it works now then that's good news and I'll get around to changing the other cats I maintain eventually
@Kohato stormfangs would be more interesting if I didn't own a stormeagle and wanted wolves for more than long fang and whirlwind access :P
@CrusherJoe, in addition to what @Kohato showed above, it's now better to do the weapon constraints on SSEs and then link them into the SSEG so they don't need manual editing. Take a look at the SM relics for examples.