How and when to prune variegated holly trees?
Most hollies are shrubs but can get rather large and tree-like without regular pruning. While most pruning is done in December, you can still prune now but it may affect the number of berries produced this year. Hollies, as with most shrubs, can be pruned back by a third of their growth. Any more than that will likely harm the plants. This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/holly/trimming-holly-bushes-how-to-prune-holly-bushes.htm