Yes, this is possible and not very difficult. By using tile molester you can extract files from the rom using Tinke to edit specific sprites and there palettes. If you follow this guide you should more or less get an idea of how to edit the sprites. The only downside is that I don't think there is any documentation for specific sprites done for squeak squad. The guide I posted is for KSSU, but I tested it for Squeak Squad and it works mostly the same. If you have any questions you can join the KSSU discord and I will gladly help.