Synonyms for interpolate

Most common

1. Alter

alter, falsify

Other

insert, introduce, transclude, foist, intercalate

v. 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

Past participle: interpolated
e.g. interpolated → altered, falsified, inserted, introduced…

alter As the artist grows older his paintings may alter.
falsify I will falsify a permit so that I can go camping there this weekend.
insert Insert the VHS tape into the slot, and press play.

Use in printed books, per decade from 1850 to 2019.

The small number after each word is its number of syllables (alter² = 2 syllables).