You need a UTF editor and BiniQDU (or other ini editing tool - but i find this one is damned easy to understand for starters!)
This is the lazy man way of doing it.....
Open up the relevent CMP file for the ship (ships folder - then go to the type - ie for Valk its in rheinland and called the rheinland elite) with your UTF editor. Look for the little +/ sign - click on that to expand the thread. Now cos i don't know which ship you are looking for here - you will just have to open each subsection in turn - looking for a hardpoints, then fixed (fixed, revolute and another one - am going from memory here) When you find one for HpThruster01 or something you have the right thread. Make sure that the thread containg the HpThruster and others is highlighted (parent thread of all the entries for fixed and make a new node (add node) select that node name it HpThruster02 and then add two more nodes to it..Name these as orientation and position (make sure you spell em right) now edit both these and copy and paste the values for the HpThruster01 orientation and position.
Save and then use biniq to open the shiparch.ini
Scroll down to your ship - then declare the extra hardpoint like this

hp_type = hp_thruster, HpThruster01
this will become
hp_type = hp_thruster, HpThruster01, HpThruster02

Save and go mount your thruster - you will go faster - but the drain will be larger as well - so it balances out overall...........

Don't think i missed anything - just make sure that you back all files you mod up first....you have been warned! lol
Chips