Current questions and answers regarding the map editor.

<7Legion_5_Creature_Tier>7
<7Legion_5_Creature_Count>1

That's not it at all; these variables are stored exclusively in the executable file. But yours isn't there, and it can't be.

It's not a problem for me to replace someone's ID; I just need to know where and what to change it to.

Leave the ID of an existing set (I would take, for example, the lion set; it is very close to yours in "spirit." Or you can take the runic set because it has the most questionable bonuses, in my opinion) and assign new artifacts to it in place of the old ones (or you can assign some of your artifacts + leave what is already there).
The initiative bonus of the lion set can probably be adjusted in DefaultStats (check if there is such a parameter there). Adding a 7th-tier creature can only be done through scripts.