Going into game properties every time and adding these launch options then deleting, may be annoying:

Europe:
-address eu.actual.battle.net

Americas:
-address us.actual.battle.net

Asia:
-address kr.actual.battle.net

Workarround:
• Steam -> Add Non Steam game (d2r.exe, can be found by clicking browse local files of D2R from steam library)
• Add launch options for that game, listed above and rename it to D2R Eu, or D2R Americas for example.

Optionaly you can add all 3 shortcuts on your desktop for quick trading, your main game and 2 other regions, and you won’t be earning any achievements obviously, until you launch base game.