AERC
Pointing you to the AERC again… Read the whole rule book before you compete, and become a member to be “official.”
You sign up with the correct weight for yourself plus your tack when you become a member and that’s what it’ll be in competition. If you are right on the cusp between weight classes, you may have to change your class the day of the ride depending on your weight and tack that day.
Some weight loss during a hard ride can be expected but even if you changed your saddle pad, it really shouldn’t be that much.
Also, you are just starting out so you’ll probably be doing limited distance (25 and 30 miles) for a while. There really shouldn’t be any need to change your saddle pad - or even your saddle!? - at the one vet check you’ll encounter.
From the AERC rule book:
8.5.2.1 Heavyweight, consisting of riders whose combined body weight and tack is 211 pounds or more.
8.5.2.2 Middleweight, consisting of riders whose combined body weight and tack is from 186 to 210 pounds.
8.5.2.3 Lightweight, consisting of riders whose combined body weight and tack is from 161 to 185 pounds.
8.5.2.4 Featherweight, consisting of riders whose combined body weight and tack is 160 pounds or below.
8.5.2.5 For a rider to stay within a weight division he/she must meet the minimum requirement but need not stay under the
maximum parameter.
8.5.3 Each rider riding for weight division points may be weighed at any ride.
8.5.3.1 Any other rider has the right to challenge the weight of a competitor and request a weighing.
8.5.3.2 Management must exercise reasonable discretion in making allowances for normal weight loss of rider during competition
and inaccuracy of ride scales. (A 4% allowance applied evenly to all competitors would be reasonable.)