I claim the ornamental design for a perimeter slider clip for mounting wall panels unto a track mounted unto an existing wall, as shown and described.
FIG. 1 is a perspective view of the perimeter slider clip for mounting wall panels unto a track mounted unto an existing wall, showing front, right and bottom sides in accordance with the present design;
FIG. 2 is a perspective view showing front, left and top view thereof;
FIG. 3 is a bottom side elevational view thereof with the top side elevational view being a mirror image thereof;