Yes

                promotion.RedemptionLimits.PerPromotion = int.MaxValue;
                promotion.RedemptionLimits.PerCustomer = int.MaxValue;
                promotion.RedemptionLimits.PerOrderForm = 2;

Doesn't that just set the redemption limits? I need to add redemptions to a promotion not change the redemption limits.

I see, then in that case, no. PromotionInformation which is used to determine the redemption is tie to a specific order form, you will gonna mess that order form promotion up if you add more entries to it.

You can, in theory, write your own RedemptionLimitService to return how many redemptions left for a specific order, other than its actually recorded number. However I don't know how your promotions are shared, so it could be tricky.