Disclaimer: I am just telling you what to do, if you want someone to write the code for this for you, hire them to do it… we don’t make things for free. (Not saying you’re asking for this, but I’m just giving you a heads up.)
For the morph:
You will need to determine what the CFrame offset from a limb to a morph piece should be, and then weld a clone of said morph piece to said limb with said offset as its C0.
You do this for all the pieces of the morph.
Note: do this in a server script
For the rank check:
Check the player’s rank in a group using Player:GetRankInGroup(GROUP_ID), and compare it to the minimum rank you want them to have for a specific morph. If they should have said morph, apply it using the method described above.