Is it possible to not show units in the "Select - Dimension Value" box? If this is possible it would then allow you to add, subtract, multiply or divide in the "Select - Dimension Value" box without having to remove the "mm" first.
Solution
Yes, it possible to not show the units in the "Select - Dimension Value" box.
In the Part environment go to the Solid Edge Options. In the General tab uncheck "Show units in value fields".
This should give you the desired behaviour e.g. the ability to start typing inline calculations without first having to remove the units.
Notes and References
Hardware/Software Configuration
Platform: INTL64
OS: window
OS Version: 1064
Product: SOLID_EDGE
Application: PART/SHEETMETAL
Version: V219.0
Function: DIMENSIONS
Ref: 002-7009695