I am sorry but I don't get your question.

vec2d_rotate rotates a two-dimensional vector from its origin (x:0,y:0), same as vec_rotate does on a three-dimensional vector.
Code:
vec2d_rotate(v,ang) === vec_rotate(v,vector(ang,0,0))


In my last code example I computed the center and the bounds of a rectangular prism from two world space vectors considering the prism aligned to carthesian planes, then I rotate two simmetrical bounds vectors, been their origin the center of the prism.

Code:
VECTOR vMax, vMin;
vec_set ( &vMax, vector(400,200,200) );
vec_set ( &vMin, vector(0,0,0) );

VECTOR vCenter, vBounds;
vec_lerp ( &vCenter, &vMax, &vMin, 0.5 );
vec_diff ( &vBounds, &vMax, &vCenter );

...

VECTOR vP1, vP2;
vec_set ( &vP1, &vBounds );
vec_set ( &vP2, vector(vBounds.x,-vBounds.y,-vBounds.z) );
vec2d_rotate ( &vP1, nRotation );
vec2d_rotate ( &vP2, nRotation );