I am probably a bit late in commenting, but jAA has a meaning in Classic Betza notation (an Alfil-jumper-rider, i.e. a piece needing hurdles for each Alfil step it takes), and changing that meaning to something very ad-hoc is probably a bad idea. Either adding a new lowercase letter for slip-movement or attempting for a generic solution with different types of movement in the two legs of the move as in Betza's proposal t[FAA] would be better. Or new uppercase letters for the atoms slip-Rook and slip-Bishop.
I am probably a bit late in commenting, but jAA has a meaning in Classic Betza notation (an Alfil-jumper-rider, i.e. a piece needing hurdles for each Alfil step it takes), and changing that meaning to something very ad-hoc is probably a bad idea. Either adding a new lowercase letter for slip-movement or attempting for a generic solution with different types of movement in the two legs of the move as in Betza's proposal t[FAA] would be better. Or new uppercase letters for the atoms slip-Rook and slip-Bishop.