Hi Peter - Great question. You can add your own calibration points to your network using the following procedure:
1) Once you've loaded your network, do not run the Update Calibration GP tool (Choose No when prompted after polyline loading).
2) You'll need to prepare your existing calibration points to match the Calibration Point feature class you've modeled as part of the ALRS minimum schema. One method to do this is to create a staging feature class modeled similarly to the calibration point feature class used by the ALRS. Our documentation provides guidance on the required fields for calibration (ALRS data model—Roads and Highways Desktop | ArcGIS Desktop).
3) Once you've created the staging feature class, use a Simple Data Load (SDL) operation to load your calibration data into the stage feature class field mapping the route ID and measure information. Optionally, you'll also need to be sure your temporal fields (From Date/To Dates) are mapped if you are loading multiple timeslices of roads.
3) Once you've populated your calibration point staging feature class, look at the dLRSNetworks domain in the GDB. Since Roads and Highways is capable of supporting multiple LRMs you'll need to field calculate the calibration point feature class field called NetworkID as whatever network coded value domain matches the network you're currently working with (most likely "1" if you only have one network).
4) Once you've populated all the required field information into your calibration point staging feature class, simply SDL your stage data into the Calibration Point minimum schema object.
5) Right Click on your ALRS network and choose Generate Routes.
Of course, you could streamline this approach by simply loading your data into the Calibration Point feature class directly and just applying the field calculations for temporality and NetworkID rather than staging the data. I just sometimes prefer staging data and making sure it is exactly as I want it before I actually push it to R&H. Should you wish to discuss more complex data loading procedures and best practices just reach out to the Esri Transportation Team. Thanks!
-Amit