Page 3 of MaelstromSetup.pdf is the key (with screenshots) to launching a particular game. Edit the Maelstrom ERAS 2 shortcut and make sure that Target: is the full path on your machine (wherever you installed the Maelstrom files) to the Maelstrom.exe you want to play (e.g. C:\Maelstrom\gentlemen-of-fortune-maelstrom-engine\Maelstrom.exe); your path may be different.
Make sure the Start in: is the path where the ERAS files are (i.e. the directory that contains the Programs, RESOURCE and start.ini files for the mod). Example: C:\Maelstrom\games\gentlemen-of-fortune-historical-eras-module-2
Click OK after you change those two paths. Double-click the Maelstrom ERAS 2 shortcut you just edited. It should launch the game.
If you did not put the game in the suggested directories, then unfortunately the Itch process does not allow for on-the-fly editing of the shortcuts and .toml file that drives their client launcher, so you will have to either edit the .toml file for the Config to work, or you can also make a shortcut for each mod Config. There is also a sample shortcut provided you can edit, called: Maelstrom ERAS 2 Config Example
Change the properties for the Target and Start in.
Target for sample: C:\Maelstrom\gentlemen-of-fortune-maelstrom-engine\DirectX9_32bit\Config.exe "..\\..\\games\gentlemen-of-fortune-historical-eras-module-2" Change this to
Target: C:\MypathforMaelstrom\DirectX9_64bit\Config.exe "C:\mypathforERASstuff"
Start in: C:\MypathforMaelstrom\DirectX9_64bit