The surge tank is easily paintable. It's ABS plastic and it should never see temps hotter than the coolant inside. There are three hose connection under it along with a sensor for the low coolant light. Once the hoses are off, it is easily removed from the bracket. There will be a fair amount of coolant in the tank and the hoses and heater core so make sure you have a way to contain the coolant.
This might be a good time for a coolant change and perhaps new hoses if you haven't done them. OEM Heater hoses are expensive so you might want to consider the upper and lower radiator hoses and the small TB bypass hose.
Use 320grit paper to roughen the surface, clean with a prep like Prep-Sol and use a good primer. Finish with either body color or whatever color looks good!!