I've seen introduction of seashore paspalum to bermudagrass, and manilagrass to bermudagrass, by hand planting the introduced species into slices cut into the exisiting turf. This post shows seashore paspalum planted into a bermudagrass fairway using that technique.
I've also seen resodding to convert to a different grass, but in a way that doesn't require course closure.
At PGA Catalunya, hybrid bermudagrass was introduced into the creeping bentgrass fairways. These photos show the fairways in 2016, five years after the bermudagrass was added.
The idea was to improve fairway conditions in summer with the bermudagrass, due to the poor irrigation water quality. I've been impressed with the fairway conditions at PGA Catalunya, and also with the technique used to introduce the bermuagrass. These videos of the technique are shared on course superintendent David Bataller's YouTube page.
What technique was used at PGA Catalunya?
First, simulated divots were made in the bentgrass fairways using an aerifier fitted with custom "tines".
Second, a rotovator or landscape tiller was used to make a divot mix from certified Tifway 419 sod and sand.
Third, the divots in the bentgrass fairways were filled with the bermudagrass divot mix.
The result is improved fairway performance during the summer, due to the presence of bermudagrass. And with this technique, the improvement was accomplished rapidly, without closing the course, and used a relatively small amount of purchased sod.