Ok, so you want the following rels to turn into different rels:
st_metalgear.rel
st_dxpstadium.rel
st_tengan.rel
Ok, so first thing you need to do is download
HxD Hex Editor.
Once you have that, open it, then open your rel. For example, lets say you want to make st_tengan.rel into st_final.rel, so open that up in HxD.
What you need to do next is very simple; you need to find this string of hex: 38 A5 00 00 38 80 00 15. To find it, go to Search > Find, and make sure the Datatype box has "Hex-string" in it, and type in the string of hex I just showed you in the "Search for" box, then click "OK".
It will find and highlight that whole string, and now what you have to do is replace 15 -- the ID of Spear Pillar -- with the ID of Final Destination's, which is "02". So, your string should now be 38 A5 00 00 38 80 00 02.
Go to File > Save as... and save it as "st_final.rel". Place it in your pf/module folder, and make sure you also have STGTFINAL.PAC in your pf/stages/melee folder as well. You should be all set now.
For more information, visit
here.