Natively you'd have to do something like this:
Begin Text Compare : [{CMDSEGMENT:1}] Equals 'Front Line'
Set Text [consoleCommand] to 'FL'
Else If Text Compare : [{CMDSEGMENT:1}] Equals 'Skirmage'
Set Text [consoleCommand] to 'SKM'
Else If Text Compare : [{CMDSEGMENT:1}] Equals 'Team Death Match'
Set Text [consoleCommand] to 'TDM'
Else If : [{CMDSEGMENT:1}] Equals 'Deathmatch' OR [{CMDSEGMENT:1}] Equals 'Free For All'
Set Text [consoleCommand] to 'FFA'
Else If Text Compare : [{CMDSEGMENT:1}] Equals 'Horde'
Set Text [consoleCommand] to 'HRD'
Else If Text Compare : [{CMDSEGMENT:1}] Equals 'Battle Royal'
Set Text [consoleCommand] to 'BR'
End Condition
Set Text [consoleCommand] to 'ChangeLevel {TXT:consoleCommand}_{TXTREPLACEVAR:"{CMDSEGMENT:2}":" ":"_"}'
Press ~ key and hold for 0,01 seconds and release
Quick Input, '{TXT:consoleCommand}'
(I don't know how the actual game takes commands, just pressing tilde as an example)
If the console commands are case sensitive, you'll have to use a condition tree for the map names as well as the modes.
Otherwise you'd have to use an inline function that does the lookup instead; I've used dictionaries or multi-dimensional arrays for this before.
If you don't want to deal with the downsides of variables in command names, it's also handy to have the inline function output the full command string to the clipboard, so you can just paste it into the "When I say" field.