Sourcing a product from China

I have an idea for a product that is very similar to some existing products available on Alibaba but with one or two custom changes like using a thicker plastic or painting a different color.

Does anyone have any experience in dealing with Chinese suppliers and asking for changes to be made to standard products? I imagine that it would raise the minimum order for the new product but I would be interested to hear if anyone has gone through this process.

Many thanks.