Can you possibly make it to where when you create a monster that its proficiency bonus isn't tied to the challenge rating(CR)? For example creating a monster that doesn't meet the other criteria such as HP and damage die to be a CR 17 has to be marked as a CR 17 during creation if you want it to have a +6 proficiency added.

This would go against rules as written and, as such, D&D Beyond are unable to make something like this happen. They have to stick to the way WotC has laid out all aspects of the game.

Now, having said that, you can apply additional modifiers to skills, attacks, and save DC as those aren't automatically parsed by the homebrew system.

Quote from 1WngdAngel >>

This would go against rules as written and, as such, D&D Beyond are unable to make something like this happen. They have to stick to the way WotC has laid out all aspects of the game.

Now, having said that, you can apply additional modifiers to skills, attacks, and save DC as those aren't automatically parsed by the homebrew system.

 
Sort of. It's a homebrew tool so D&D Beyond are free to allow anything they want. They are entirely free to allow people to override absolutely anything they want. The issue is simply they didn't think of allowing a way to override it, nor did they future-proof the code.

The issue isn't "can they", the issue is "will they". 

The monster homebrew tool is woefully inadequate and doesn't match WotC publishings anymore since "no-CR" monster statblocks are now an official thing (the summon spells, among others, create statblock monsters that do not possess a CR but can have anywhere from +2 to +6 proficiency. The lack of a CR (which is different to a CR 0) was a deliberate design choice, making it so you cannot transform it or yourself into one) but the monster tool will simply not let you make one.

So saying this site has to enforce the game rulings in all homebrew creations "because it's the game rules made by WotC" isn't a valid argument for a homebrew system. Especially when WotC don't agree with it as evidenced by lines in the DMG such as "the DM interprets the rules and decides when to abide by them and when to change them." and "The D&D rules help you and the other players have a good time, but the rules aren’t in charge. You’re the DM, and you are in charge of the game." 

The restrictions put in place are therefore largely against the spirit of the game that literally tells DMs they can change rules to what they want.

Quote from 1WngdAngel >>

This would go against rules as written and, as such, D&D Beyond are unable to make something like this happen. They have to stick to the way WotC has laid out all aspects of the game.

Now, having said that, you can apply additional modifiers to skills, attacks, and save DC as those aren't automatically parsed by the homebrew system.

 1WingdAngel,

You stated that "you can apply additional modifiers to skills, attacks, and save DC as those aren't automatically parsed by the homebrew system".
I am creating a monster that I need to modify the Str Save DC, and cannot figure out how to do that, can you explain?

Thank you!