As long as you keep them short, there shouldn't be a problem. Religious pruning slows or arrests root growth--one of the things that makes bonsai possible.

As long as you don't let them go like the 'conifer rage' articles in the papers recently!!!! Have a look at 4 seasons garden blogs . They keep conifers scattered in their garden constantly trimmed. As TG says above you can be in control not your plants.

Our conifer expert is member Bluespruce, he'd be able to advise on them with great authority, send him a PM, why not.