I've never had a problem with giving them a trim this time of year. Your only issue may be that trimming may cause them to flush with new growth, which you will have to trim again.

The 'Kleim's Hardy' gardenia certainly has the fine fragrance of gardenia, but don't you think its flowers are pitifully ugly? I recommend that you pull the plant up and throw it onto the compost heap. Then, replace it with a 'Chuck Hayes' or 'August Beauty' gardenia that will reward you with both the pleasing perfume of this species as well as tradtional, beautiful double blossoms.

That is true about trimming and stimulating new growth. What I may try is to totally remove some of the side branches. I will also have to think about moving this plant. Replacing with "Chuck Hayes" is also a good thought. Thanks for the feedback.

I have been forced, due to heavy snow having bent them to the ground, to prune my klein's hardy gardenias by half on some years. Ideally I would suggest trimming 1/3 of the branches by as much as half or more each year (think of thinning it out) so that after three years you have a much smaller bush.
If you are actually considering replacing it, what do you have to lose by pruning it very hard and see what comes of it?