Uh, as a general rule, you have to be careful changing the size of an object with the scale tool. It happens to work on the length of simple extrusion, but it’s a problem for other things like a double hung window; if you scale the whole thing to change the over all size, all the internal parts are scaled up proportionally. For that reason, my go-to tool for this type of task in general is the move tool.
•If it’s a component, make it a new, unique component so you don’t mess up any other instances already in use.
•Open the component or group.
•Select the geometry for the end.
•Use the move tool and move the end by the amount needed.
If it’s a 40cm tube and you need 50cm, then move the end by 10cm. Note that if the flanges of the tube were, say, rabbeted 1 cm back from the end, scale would mess that up, but if you use a selection rectangle to select all the end parts and move them, you preserve that relationship.