You can use negative numbers in the "Add Exp" function too. I did that and was able to get the other achievements this way.
We can "de-level" using this method?
Yes u can, just put - infront for the number and hit 8 that many time u need to go back to the lvl u want. if u are lvl 40 u can use -50000 a few times. remember to change it when you reach the lvl u want. i did go back to lvl 4 and did kill a few animals to reach lvl 5. then i did use 8 again to reach lvl 9 to kill a few more to reach 10 and same for lvl 19. i dont think there is any archivements above lvl 20 but if there is i need to go back again :P u can also remove attribute points. and the funne part is that u can gain lvl 40 and get those gold items and then go back to the lvl u want and still use lvl 40 items, u only loose some health.
Some of them probably can't be done or are not necessary, for example:
"Toggle Bayek hair and or beard options" can be done in-game
and " Alter Quantity of Crafting Materials or Items" can be done with CheatEngine or CoSMOS.