To search and replace substrings or complete texts in an AutoCAD drawing, including an option to use scripts and replace texts (and dimtexts and attribute texts) in many DWG files at once, you can use the free/trial CADstudio's utility - srxTEXT. For search and replace you can also use regular expressions and perform even complex text replacements of the type:
D19-457-03667 --> Part:457/03667 Code:D19
or add strings to the beginning or to the end of your texts or individual words, or replace only a single/first occurrence of a substring, etc.
You can also use scripts to replace texts in multiple drawings (batch mode). Replace strings defined by search-replace pairs loaded from an Excel table (CSV file; the srxTextCSV command).
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