Open up MCM and go to the Mod Construction tab, click on Add New mod to Library and in the "title" field type "Omega stage Toggle", in the "author" field type "_glook, TDRR" in the "description" field type "To switch to the Target Test stages, press R at the Stage Select Screen, you will hear a sound and the cursor selection border color will change to purple, press L to switch back to normal.
-Venom = Pikachu's target test
-Flat Zone = Link's target test
-Icicle Mountain = Bowser's target test
-Poke Floats = Kirby's target test
-Rainbow Cruise = Peach's target test"
Then click on the plus sign beside "Injection mod" and on the "offset" field type "0x256FA4" then select the thing that says: "Type: Injection (0 bytes)" and on the text field on the right paste the code in the above post named "Toggle between alpha and omega at SSS" then you need to press the plus sign beside "Injection mod" again to add another one, this time you need to type "0x256FA0" and select the new box that says "Type: Injection (0 bytes)" and paste the code in the above post named "Display Unique icon borders at SSS" on the big text field
NOTE: Don't put quotes and don't copy the part that says "Injection point: blablabla" because that's an instruction for you, not MCM.
And finally click the Injection Mod plus sign again and on offset type "0x258720" select the box that says "Type: Injection (0 bytes)" and paste the code named "Omega toggles for some stages (MELEE XT)" press save and save it in any TXT file shown to you, i recommend Stage Select Screen as it's the most obvious place, but put it wherever you want.
Click the button on the high part of the window that says "Open" you will then be prompted to select your .iso file, browse for it and then open it.
Now just go to the library again and choose the tab corresponding to the folder you chose, you then have to select the code you inserted into the library, which is at the bottom of that tab, click on it and it should become green, just click save, wait for the process to finish and you are finally done!
If the game crashes, please tell me so i can help you fix the issue.