The problem is i would like to create a swap for a new altcoin that's not on shapeshift list, is it possible to users insert new altcoins by working on the API code?
No there is no such API that can be used to code automatic bitcoin to any altcoin exchange like shapeshit is using currently. You can although suggest shapeshift to add that new altcoin in their lost.
Another option could be you can open a manual exchanger site where you have to manually send bitcoin or any altcoin as owner. However creating this type of manual exchanger need you to hire dev with enough html, php, mysql, java and ajax knowledge atleast.