It's generally not a problem to just add  another parameter  and then in
the function  call on the sheet point it at a specific cell.

For example, if the function is...

Function fncMyFunction(sp1 As String, bl2 As Boolean)
MsgBox sp1
MsgBox bl2
End Function

Then this...
=fncMyFunction("Test",C1)
....in A1 and TRUE in C1 will report "Test" and TRUE.