Better to just buy the DLC that comes with the Uk Edition. The base simulator is the same between the two versions so there is no need to buy it twice.
If you got your NA edition through Steam, there is a big sale on the full edition, the regional editions and all the bundles of DLC starting this morning. Check it out. I don't know if N3V is having a sale.
I think if you buy another edition all that happens is your account is flagged for owning that product meaning you can then download the additional content which will show up in the in game download window of your current install. Since the TRS19 app is the same, there is no need to re-install the app. Just download the new assets that you want. (The only difference between "regional editions" are the Routes that are included.)
