CTR+ENTER is already taken. Select a range of cells, press F2, enter your formula, CTR+ENTER applies and fills that formula to the whole range (very useful).
Normally the first one commits the formula, the second one inserts a newline. I want to reverse that and make a naked [Enter] insert the newline, and the [Alt]+[Enter] commit the formula.
Committing a formula needs to be a simple shortcut because it has to be used by the least technical users. You don't want to create a "how to exit VIM" mess in a retail product.
#if IsExcelFormulaBox() ; Whenever the formula edit box has focus
Tab::Send {Space}{Space}{Space}{Space} ; insert four spaces when I hit [Tab]
$!Enter::Send {Enter} ; commit the formula with [Alt]+[Enter]
$Enter::Send !{Enter} ; insert a newline with bare [Enter]
#if
IsExcelFormulaBox() {
ControlGetFocus, F, A
return (F="EXCEL<1")
}