How to set unit stock/recharge speed (in a shop)

Can this be done via triggers (Instantly setting a unit stock and recharge speed)? if yes how? If not, how can i apply "Dependencies" to bought units? Like you cannot buy the unit before you own X thing.

Stock replenish speed can be altered with a field in the object editor for the item (Stock replenish interval). I don't think this can be altered with triggers.

To add conditions to buying things (at least the way I do it) is put the item gold cost as the point value of the item (object editor) and make it so that if the buyer does not meet the condition, then add the point value of the item to that players gold (to return the cost) and remove the purchased item from the game. The only problem with this is if you want to have a limited supply of the item from the store with a slow restocking interval.