Felt will make the pumpkin turn faster, since they don’t like clothes.

For real, though, plants need to breathe, and they breathe through their skin – if you block their pores with glue and fabric, they’ll go off faster.

Paints aren’t as bad, though they’ll also block their ability to exchange the gasses (ethylenes) that need to escape. If ethylenes are trapped, the veg will turn much faster. This is why you can buy ethylene exchanging bags and containers to keep your produce fresh longer.

The only way to keep seeds and pulps from turning is to gut the pumpkin before decorating it.