I created a custom InfoPath list-form, added all the controls, created all the rules etc. and now it seems I'll have to add some code-behind into it. Is there any way to convert the template type or at least copy all the things I've got into the new project?
I don't think it is possible to switch between templates , you can check this link for more information : https://sharepoint.stackexchange.com/questions/52675/infopath-2010-sharepoint-liist-form-and-custom-code
However you can copy InfoPath controls from one form template to another but only if the control contains data that is a part of a view, here's how :
check this link for more details : http://www.bizsupportonline.net/infopath2010/videos/copy-control-one-infopath-form-template-another.htm
for copying the rules i don't think there is an easy way to do it but here's how :
for more information check this link: http://devspoint.wordpress.com/2010/10/25/copy-infopath-rules/