Alternate date for use in deprecation calculation

[brutal-dismount]

Currently purchase date is used to calculate deprecation. Since purchase date and deprecation start date don't align with our business model of using in-service date, leveraging another date for this calculation would be beneficial.
I currently get around this by using the "purchase date" field as the "in-service date" and creating a custom date called "real purchase date" where the actual purchase date is placed. It works, but is confusing to end users when creating/reviewing new assets.

It would also work if changing that label on "purchase date" was allowed. Then I could change the label of the purchase date to "in-service date" for use in deprecation calculation and also creating a custom date called purchase date.