Excel by default will change percentages to decimals so arithmetic can be used on them. Are you not able to do the same and treat all your percentages like a decimal? (.765*100 = 76.5)
If you want to keep the % character and treat it like a string instead with the original data, then you would need to originally store it wtih a ’ character infront… I think.
The other option is to store the original data in a CSV where the format is maintained. EDIT: And, if you are saving the data to a new file, then you would want to format the columns the way you want, then save as a CSV, and the formats will be maintained.
To be honest, though, I would just treat the % like a decimal because % should be a number. Basically, when you filter it just filter it based on the percent as a number (like Percent<.8, which would be less than 80%)
But, it’s up to you on how your approach this.
Let me know if you need further ideas.