If you want to rotate it by 90° turns, rotating the tilemap is quite easy: you just add a modified subroutine to acces the tiles with the x and y coordinates swapped. And if the result is mirrored, substract one of the coordinates from 15.

To rotate the sprites themselves, it may be a bit harder, but since 4*4 sprites don't take up much space, it might be best to just save the rotated sprites as well. Just add them right after the normal tiles, in the same order (so they are at a fixed offset to the normal tiles). Then, to acces the rotated sprites, just add that offset to the pointer of the normal sprite.

If you want to rotate the tilemap by a certain amount of degrees, it will be a lot more complicated, and I don't know exactely how it should be done.

i agree that you dont really have to rotate the actual map data in place, rather just read from it differently and rotate the sprite data when its draw in accordance.

For rotating tiles, of course, there's rotc() and rotcc(), but I would recommend preloading rotated versions of each sprite somewhere like L1 (if the spritesheet is not too large) so it's faster to draw rotated sprites. Otherwise there might be a visible speed drop when the map is rotated, as the program would have to calculate rotated sprites on-the-fly.

Then your only option if you don't want a significant speed drop is to store them as separate sprites and use a variable that tells you the orientation of the tilemap.