Hey ndog232,
Congratulations on finishing Year 12!
I may be wrong, but I am pretty sure that the Monash Guarantee is not inclusive of any SEAS adjustments and it is only for your ATAR.
So your ATAR of 74.7 will most likely not suffice, as you need a 75 ATAR (not Selection Rank) or above to get in to your course through the Monash Guarantee.
So, pretty much your additional aggregate points are not considered for the Monash Guarantee.
They will accept other students eligible for the Monash Guarantee with 75+ ATARs.
But don't let this worry you, Monash may make exceptions this year and accept lower Selection Ranks due to lack of international students (2020's Lowest Selection Rank for BSc was 85).
I hope I was able to help, please let me know if you have any more questions
EDIT: Sorry I forgot to include some things.
1. Don't change around your preferences if you are worried, you never know what can happen. Many events of this year have been unexpected!
2. If you don't make it into BSc, there are a million other pathways! Check out this link:
https://www.monash.edu/science/future-students/pathways/pathways-in-to-scienceThe Diploma of Higher Education can be completed in a year at the Clayton Campus. You can complete the science stream which will lead you into second year of BSc at Monash, if you maintain an average over 60% and pass all units
I wish you all the best