Toyed with alias a bit with the following results.
Alias is not a variable, it's simply a shortcut for a command sequence. Anything right of the colon is not processed prior to being assigned to the alias. It is only processed when the alias is called.
Macro
alias main_tank:%t
Targeting a player named Mike and hitting the macro does not produce
main_tank = Mike
If you setup a 2nd macro
assist main_tank
this is equiv to...
assist %t
not
assist Mike
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