We claim the ornamental design for an interchangeable thermostat cover, as shown and described.
FIG. 1 is a front perspective view of an interchangeable thermostat cover;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a left side elevational view thereof; and,
FIG. 7 is a rear elevational view thereof.
The broken lines in the figures are for the purpose of showing environmental structure, are for illustrative purposes only, and form no part of the claimed design.