Without knowing what specific lenses you have, it's impossible to tell whether it's possible to switch the mounts. However, it's *likely* what you want is not possible if you also want to have a functional lens.

Which Pentax and Canon mounts? For electronically controlled lenses, I wouldn't bother. For old mechanical mounts, maybe. But the aperture control lever on PK and FD mounts work opposite each other. FD is open by default, and the pin closes it. PK is closed by default, and the pin opens it. So internally, even for the "same" lens models, the mechanics can be different so that mounts cannot be switched.

The different default aperture position also explains why some adapters are more complicated than others.