Can you cut plastic shells?

[Mermaid Tuwala]

So, the plastic shells I order on ebay for making a top arrived today. I searched for hours and ordered the smallest ones I could find but they are still way too big. Has anyone tried trimming and sanding the edges of those plastic shells? I'm worried the shell might snap or be ruined if I try.

[Mermaid Momo]

I would say yes, just very carefully and depending on how thick they are

[Mermaid Tuwala]

Okay thanks!
Yeah, I'm just worried about what tools to try and hoping it doesn't crack :S

[PearlieMae]

A photo would help. Removing material with a sanding drum on a rotary tool (Dremel) would probably work best.