Follow these steps in MeasureTool 5:

1) Open the first measurement file in MT5.
2) Open the second file in MT5 and select menu 'Edit/Copy'.
3) Bring the first measurement file to front and select menu 'Edit/Paste'.
4) Save the resulting file.

Since MeasureTool 4.1.5, the measurement files also contain the appropriate reference data. When copying the files together, this reference data will also be copied. So when dragging the new measurement file to the wizard of ProfileMaker 4.1.5 (or higher), both the measurement and the reference part will automatically be loaded.