Interpolate

verb

1. To introduce (something) between other things; especially to insert (possibly spurious) words into a text.

   "in verse 74, the second line is clearly interpolated"

2. To estimate the value of a function between two points between which it is tabulated.
3. During the course of processing some data, and in response to a directive in that data, to fetch data from a different source and process it in-line along with the original data.