Step 1: Back up your save file. There isn't really much you can screw up here but it's better to be on the safe side.
Step 2: Download MHW Transmog https://www.nexusmods.com/monsterhunterworld/mods/43
Step 3: Drag the contents of the MHW Transmog folder into your Monster Hunter World directory. ("steamapps\common\Monster Hunter World")
Step 4: Start Monster Hunter and equip any full set of layered armor. I recommend using Direwolf. The armor you choose will not be overwritten.
Step 5: After equipping the layered armor, run MHWTransmog.exe in your Monster Hunter Directory.
Step 6: Enter the slot your character is saved to.
Step 7: Enter 6, then enter 485 to apply Claire armor to all parts.
Step 8: Travel to the research base, or any other area, then travel back to Seliana. After you return to Seliana, the armor should appear.
Step 9: Register the layered armor set under the "Layered Armor Settings" menu at the item box. This will allow you to freely equip and unequip the layered Claire armor whenever you want.
Step 10: Enjoy your layered Claire armor. You never have to repeat this process again and you will have the armor forever.

If you are having trouble, here is a video guide.