Good Problem to Have: 5 Round tournament w/ too many players

I am  the sponsor of our high school's chess club and we are sponsoring the only chess tournament in the area next weekend.  Unfortunately, it is not USCF rated--although we are playing as if it were.  Coming out of COVID, we felt getting everyone to pony up $10 for a USCF membership was a bridge too far.

We sponsored this tournament in 2019 before COVID.  Then, my high school section had 32 players.  Fortunately, we planned for a 5-round tournament so this worked great.

This year, I have 46+ players.  My elementary and intermediate/middle school sections are not nearly this large.  

I know that 46 players will likely give me several undefeated players which will force WinTD to tie break.  Ideally, I would have the high schoolers play 6 rounds, but the numbers for my other sections would not support this and I wouldn't want them waiting around for an hour while the high schoolers finished (for simplicity, I'm running all section rounds at the same time.)

So, here is what I'm planning to do.

I will give local ratings based upon grade.  9th graders = 900, 10th = 1000, 11th = 1100 and 12th = 1200.  Certainly this is not perfect, but the idea is that most seniors are likely to play better than 9th graders.

Then run the swiss pairing as an accelerated tournament using these local ratings which would have my seniors and juniors play each other earlier, potentially limiting the number of perfect scores by the end of the 5th round.

Does this sound at all appropriate?  If not, what suggestions would you provide.

Thanks in advance for your kind assistance.