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, probably by some unknown medieval scribe"

2. To estimate the value of a function between two tabulated points.
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.