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

* For electronically controlled lenses (EF), I wouldn't bother. The internal construction and electronics could be significantly different.  For instance some lens designs do or don't have image stabilization or mechanical apertures, depending on the target mount.

* For completely mechanical mounts...

    * The aperture on FD lenses is open by default, while PK is closed by default. So internally, even for the "same" lens models, the mounts may be different enough that they cannot be switched.  The different default aperture positions also explains why some adapters are more complicated than others.
    * The aperture rings on FD and PK lenses turn in opposite directions.  The internal construction of the lenses may be mirror images of each other.  Even if they could be switched, the lenses would have to be significantly dismantled to do so.
    * If *any* externally visible screws don't match between lenses, it's likely the underlying construction is different enough that switching mounts won't work.