I brewed a 1 one gallon version of the spiced winter ale kit last October (local NB store ingredients and Penzeys spices) and brewed it again in January with different amounts of mulling spices.
The amount of mulling spices used is very much a personal opinion.
In the 1st batch, I started with 3 grams of mulling spices. I tasted it after primary was finished and decided to split the batch - batch 1a 'as is' and with batch 1b I added an additional 1 g of mulling spices. The flavors in batch 1a were much more muted. The people I shared this batch with preferred batch 1b (with the 1g of additional spices).
For the January batch, I also spit the gallon batch into two 64 oz batches - this time with 1.0 g and 1.5 g in secondary. My initial tasting found the second batch (1.5 g) to be too much for me - but may be close the right amount for those who like more spices.
If you can sample the beer after primary is completed, you might be able to add spices to fit your taste. Or if it is too strong, @jimrmaine's advice to let it age for a number of months would be a good approach.