InfoPath took this situation into consideration and provided you with a file: Upgrade.xsl, which gives you the ability to change the form template and have older forms upgraded when they are opened in the new template.

Many times upgrade.xsl will work automatically for your needs. If not, it can be modified by hand to meet your needs. You can also do this in code if that is better for you.

Hi,

I have a form in Infopath that is being used by the
users. Now i want to add an additional feature to this
form.  I need to add an additional table to this already
existing form, and insert few more controls that bind to
this table.

Could you please let me if it is possible to do this and
how!!

Thanks in advance.
Vamsi.

Just add the fields and functionality to a local copy and then publish to
the same location the form is at now when you are ready.

Your users will just see the new form the next time they launch the form.