Before installing or modifying your resin fursuit claws, it is recommended to wash them with hot, soapy water to remove any residual mold release. Use a soft, non-abrasive cloth to gently scrub them and let them air dry completely.
Resin parts can be sanded, carved or dremeled if needed. It's best to do this outside or somewhere you can safely contain the dust, and wear a face mask. If you need to shorten, hollow out, or completely remove the base, make sure to wash them again afterward to remove any dust.
If you want to add onto the existing claw, you can use any air-drying sculpting compound. Do not use a compound that requires baking such as 'Sculpey', as heat may damage the original resin and potentially release harmful vapors. 'Fixit Sculpt Epoxy Clay' is preferred.
When painting resin claws, you can use artist-grade acrylics (such as Golden), good-quality model paints (Vallejo), or any spray paint designed for plastics. Using cheaper paints will require many more layers and may result in rubbing off the first coats. Additionally, cheap paints do not tend to be color-fast, and your beautiful paint job could end up turning muddy greys and browns. If you are doing a complex paint job or changing the base color drastically, use a coat of plastic primer first.
Some useful products to have on hand include
LePage Ultra Gel Control Super Glue
E6000 Craft Adhesive
Krylon Colormaster™ White Primer
Golden Heavy Body Acrylic
Krylon Acrylic Crystal Clear
You can find most of these products at local arts and crafts stores, hobby shops, or home improvement centers. Most products designed for plastic minatures will work well, a local hobby shop is a great resource for paints, primers, glues and sealants.