New calculated fields

[Data-Speaks]

I noticed that calculated fields have a column name (e.g. Calculation_1312313823809128) and an alias (e.g. profit margin.) Is it possible to create new calculated fields with Tableau Tools or XML hacking? If so, should I just assign a random calculation ID number, or find the highest one in the workbook and add 1 to it?

I couldn't find any documentation about what these IDs mean, or whether they're set at the workbook level, the project level or the site level.

Thank you!