painting over good paint

If you have a TA with a good paint job but want to change the color
you can paint over it without removing that previous color.
How many times can you do that? How many layers is ok, before you'd
have to strip off or sand off layers?
I mean lets say you wanted to changes colors every year. How many times
could you paint over without needing to take off some old layers?
Thanks men!  

Personally, any more than a repaint over the original paint is too many. I once bought a 78 Z28 parts car that had been painted about 10 times without stripping and there were about 4 color changes! The body lines start to lose their sharpness and look like they were molded out of melted plastic after a few layers of primer and paint. To get a good quality finish the body needs to be stripped to bare metal, inspected for previous repairs and their quality, make any repairs and prime, block sand and repaint.
Steve  
Trying to help... 'cause we don't all have to learn the hard way!

If it was a good quality paint and in good shape each time it was sanded and was done right you can go 4 layers not including primer the body lines can be cut back in by the proper sanding techniques to give them that sharp edge look but if you are unsure of what is under the paint now then you might want to strip it all the way down to bare metal but you will need to use a self etching primer or a self etching rust inhibitor on the bare metal.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

The question is why would you want to paint it every year? Pick a color you like,I'm guessing some shade of red, and let it grow on you. If you do it right the first time it should last 20 or more years if taken care of. The cost of all the paint and materials could then be used to beef up other areas of the car. If painting it every year floats your boat take the previous replies advice.  

Being a Coating Inspector (paint)I can add some insight 1 re-paint.Sanding down or stripping to bare metal is not the way to go  SODA blast if you must go to bare metal .After a proper sanding using a primer sealer is needed when doing a color change to avoid bleed thru.These products have excellent rust inhibitors.Most agree that 6-8 mils is proper coating thickness for car paint, too thick is as bad as too thin. A coating performs (lasts)better if applied as per manufacturers recomendations and not stacked with multiple coats