Can used plastic worms be recycled and poured into a new bait?

yes

Might have to start trying this

Highly recommend looking at You Tube as there are numerous provisions/instruction on open pour and injector.
Be prepared to get addicted to many ways of being creative.

My Green Pumpkin Mardi Gras Melt Downs:

It's not as easy as it seems! Plastics must me completely dry of water before heating (heating used plastics with water in them can be dangerous), and additives must added to avoid scorching.

Also different manufacturers uses different plastics, salts, and additives that remelt a little different. Ex. Gary Yamamoto Senkos have heavy salt content and are a disaster to remelt simply because there is not much plastic there, where as zoom flukes have much less salt and melt down a lot better.

Not to discourage you because it can be done, just be very careful with residual water, scorching, and toxic fumes! Someone may have a good procedure that will allow you to do it safely and effectively, in which I'm also interested!

P.S. Trial and error is a big part of lure making. Oh and remelted plastics smell like junk!

Yes, they stink!
Yes, you have to be careful to have CLEAN and dry worms.
Add a little Plastisol and Heat Stabilizer to help things out.
You have to group colors together, or it turns into mud.

Never, I repeat, NEVER remelt Elaztec Plastic Baits...

Using certain brands of plastic lures to remelt could be a bit risky but I always try. When it comes to reheating plastisol, it can be reheated many times, but always keep in mind that the more times heated the greater the change in color brightness and hue. Glitter starts to shrink and fade after the 2nd reheat and some colors bleed and tint the plastic to form another color with the plastic's original color.

I can mix most brands of plastisol and most commercial baits with them as long as I don't add too many. As of now, I probably have forty plastic chunks of plastic in the shape of a pyrex cup waiting to be remelted as well as many bags of unused plastic lures. If possible, use a fan to vent heated plastic to the outside. You may not notice the smell over time, but others do.

What he said!!!

In the case of microwave re-heating, the glitter is actually burning up. The reflective/metallic property of glitter burn like a spoon or aluminum foil. The less reflective glitter in your microwave re melts the better.

Side notes:

To test glitter burn, heat up a couple oz of plastisol until clear, add glitter (silver is the worst to reheat) let cool for a couple minutes, and re heat watching the glitter burn up into little black flakes.

Pouring clear baits with lots of flake is better to do in small batches or with plenty of heat stabilizer to give you the time you need.

As far as melting clear used baits its almost impossible. Color distortion, glitter burn, etc.