weapons expert question

so basically this skill alows one of my heroes to use a weapon that is normally not avaiable to the warband.
does this mean that I can then buy a a weapon in the trading section of the post batlle sequence whenever I want, even if it's not normally allowed for that warband type? (keeping rarity rolls in mind)

for example, with my skaven warband, if I choose the weapons expert skill for one of my night runners can I then in the ensuing trading phase buy a crossbow for that nightrunner?

The warrior may now use any missile weapon he aquires. You may buy a crossbow for him or a blunderbuss. To aquire a weapon with a 'xxx warband only' restriction, it must be captured or discovered as part of exploration or a scenario treasure.

thnaks for the answer!