Hello, Thank you for using this service. I wish to introduce myself. I am a Research Librarian with 20+ years of experience.
Researching your question and it seems that early spring is the best time to transplant a holly bush.
Root pruning is best done in early fall, to prepare for moving the holly the following spring.
December is a good time to trim the plant back but you need to know what type of holly plant you have so you do not damage the entire plant.
Maintain an even shape and trim off any dead leaves or branches. Trim to an even shape is the best bet.
They should recover if you trim the plant into a good shape and not cut too much or too close. Researching what I have found says that you should be ok with most types of holly bushes (English, Inkberry and Blue hollies).
Trimming the shape even is the best bet as most holly bushes do well with this (English, Inkberry and Blue hollies).
Consider transplanting a holly only if it is young; the older the bush, the harder it is to transplant and the less likely its chances of successful replant.
Thank you for the information. This is just what I needed to know!