Cut'n'paste stich together in Mapsource
Open Mapsource
Highlight one route
Double left click, or single right click and click 'Route properties'
Select the 'Via points' points tab
Here you will see you start point, all your viapoints, waypoints and any favourites you inserted listed out.... end in <end>
Now here goes....
Copy the ones that you want to cut out.
Now....
Open a second route and work your way to the viapoint tab, just like before.
Paste in the cut viapoints into the right place.
If you look at the map, you will see that the magenta line has gone straight between the points, no ,longer following the wiggles of the road. You will also see that it has arrows. This is helpful as it shows where the route is going and you'll be able to see if you have pasted into the wrong section of the route.
If it looks right... Bingo. Recalculate the route and the performance is over. Check it out though as Garmin may well have slipped in a smaller road or two at the splice points, just to join the two segments together.
If it looks baaaaad.....
It's probably because you have pasted it into the wrong part. It's also quite common to have the ened in the wrong place, creating a loop. you can either just undo and start again OR move the points up and down.
Each time you move one or more up and down or delete / add one, you'll see the straight magenta line moves / the direction arrow change.
Play around with it is the best tip. You really cannot break it, particularly if you use copies of routes. I learned a lot when creating assorted Wanders and / or on other jaunts over the past 15 or so years, right back to the very early versions. It takes a little practice and you are then good to go.... that's all.