I've turned entire tracks (clips that extend for the whole project) into GrooveClips to try out different tempos while composing. Works fine (but will cause artifacts in the audio until you bounce the time stretching).
You will want to be sure to trim the start and end of any clips you do this to so they start and end exactly at snap points (like measure lines). This will keep the clip/timing in place within the project.
If you want to keep the change (I usually just do this when writing then retrack at the new tempo) and there are still artifacts after bouncing the clip try a) another offline render algorithm and/or b) opening the clip in the Loop Constructor view and adding more finite (or custom) splits to get better fidelity.
Cheers.