when should I hard prune overgrown yes
Do you mean yew?
Yews (Taxus) are very tolerant of pruning as new growth will develop from old wood. Yews can be shaped by pruning through the spring and summer but do not prune in late summer or fall.Yews need to be planted in well-drained soils. Poorly drained soil (such as clay soils or soils in low areas) is the “kiss of death” to yews. Yews are very tolerant of pruning. Old yews can be rejuvenated by cutting into wood with foliage but it will take several years for the plant to regrow and assume an acceptable appearance. Due its toxicity to humans, yews should not be planted around playgrounds or other areas where children (or livestock) may be tempted to eat the foliage, bark, or seeds; the red fleshy portion surrounding the seed, the aril, is not poisonous. Deer relish yew foliage without any ill effect – too bad.
Hope this helps.