Switching an encoding can mean two different things: changing how existing bytes are read, or changing how correctly decoded text is written. Keep those actions separate. First find the interpretation that makes known text correct. Then, if migration is required, save a new UTF-8 copy and reopen it.
Reduce the candidate list before touching the editor
For older Japanese files, UTF-8, Shift_JIS, and EUC-JP are useful first candidates. Use the source system to order them, but do not decide from provenance alone. A file from an old Windows tool may suggest Shift_JIS; the text still has to prove it.
Mark ten anchors across the file, including names, punctuation, Japanese prose, and the final sentence. ASCII-only lines are weak evidence because they may look correct under several encodings.
Keep a comparison note
Open duplicates under each candidate and record which anchors pass. A note such as “UTF-8: name correct, middle prose wrong; Shift_JIS: all ten correct; EUC-JP: punctuation wrong” is much stronger than a memory that one option looked plausible.
If no candidate makes every anchor correct, stop. The file may mix encodings or already contain damaged bytes. Saving one of the imperfect views will not solve that problem.
Switch the reading in Rune Studio first
Use the tab’s encoding control to change only the interpretation while comparing candidates. Do not save during this stage. Once one candidate passes all ten anchors, record it as the source encoding.
If you need a UTF-8 working file, use Save As and choose UTF-8 for a new filename. A controlled Shift_JIS-to-UTF-8 copy reopened with matching text while the source remained unchanged. The exact pre-save warning display was outside that check, so read and resolve any warning shown by the installed application.
Reopen to finish the migration
Close the newly saved tab and open the file from disk. Confirm that it is detected as UTF-8, then revisit the ten anchors, line count, and final sentence. This verifies written bytes rather than the correct text still held in memory.
Keep the source until the UTF-8 copy has survived real use. The old file is not clutter during migration; it is the rollback point.
Decide what “switch” is meant to accomplish
If your only goal is to read a legacy document, finding the correct interpretation may be enough. If the document will be edited and shared in a modern workflow, the separate UTF-8 save and reopen are part of the job. Calling both actions “switch encoding” hides where the data changed.
Rune Studio suits hands-on comparison because candidate encodings and the manuscript are in the same workspace. Byte-level recovery and unattended conversion of thousands of files need different tools. Check current support on the Rune Studio product page, then start with three named duplicates and ten known anchors.