There are 3 scales at the bottom of the Illustrator export. The values in them are dependent upon the measurement on the system, and on the measurement in the map projection.
The first line is always the minimal measurement in system units (inch in US) vs. the corresponding value measured in the default measurement units of the coordinate reference system.
The second line is a linear value nearest the aforementioned unit vs. the system units (meters vs inches in this case most likely).
The final line is a pure scale, presuming the page is accurately reproduced.
There's currently no way to force Cartographica to change the map units without changing the Map Projection, although you can likely either find a foot/mile based Projection if that's necessary. This is the suggestion we have if you are join to be doing this often.
For many uses, and when you aren't doing this multiple times a day, changing the values in the top line can be done by changing the label and the bottom line is accurate regardless of units. However, the 2nd line must be manually modified by using the ratio of what you want to what is there and using the Object Transform unidirectional scale function to adjust for the new scale. So, if you have 100m and you want to change to 1 mile, you'll need to scale the 100m line horizontally by (1,609.344/100) or 16.09344. Then change the text.