Question:

Is it possible to modify your existing trailer into a swing away trailer?  What would be the problems?  Load capacity? etc.?

I recently purchased a house that may or may not be able to store my boat in the garage.  Just curious if it could be done...

Yes it can.  The price around here varies from about $300 to over $1000 depending on the shop that does the work.

I would also think that the complexity and cost may depend also on wheather the trailer has surge brakes or not as I have often pondered converting mine to a swing away (which has surge breaks).

I have a 16 ft. tin boat and I opted for a new trailer that came from the factory with a swing away tongue. You can have a buddy cut and weld the swing away bracket for you but there is a bit of "piece of mind" about a factory trailer. It takes a little more time to get it together in the morning but the bottom line is, it now fit's in my garage.

My trailer is for a 96 stratos.  It has no surge brakes.  My main concern was the lack of stability and safety with the load bearing.  I will have to look a bit more closely at the options as to whether or not this can be safely done.  It seems possible.