The perennials you listed, Yes it is ok to cut them back in the fall. The butterfly bush, is an early summer bloomer, so it is ok to prune back hard in the late fall or winter or if you forget early spring. It will form growth and new flower buds in the spring and flower again in the early summer.

Blue spirea - Cut back the shrub in late winter or early spring when its new growth begins.
Remove all old, dead stem tips back to the healthy growth, and shape the shrub
as desired. Prune the plant to the ground if it dies back completely
during winter or to encourage denser new growth

Blue spirea is a beautiful shrub if you can keep it alive...good luck.

Lavender is best pruned right after it finishes blooming for a second lighter bloom. Otherwise prune in November or late winter/early spring to form a mounding shape. Also prune out any really old stems, dead, or horizontal growing stems along the base.

Spring and summer care for Russian sage consists mainly of pruning. When new spring growth emerges, cut the old stems back to just above the lowest set of leaves. If the plant begins to spread open or sprawl in late spring or summer, shear off the top one-third of the stems to encourage upright growth.