These patch files allow you to generate an older version of Kero Blaster from the files of Kero Blaster v1.5.0.1a:
https://www.cavestory.org/downloads/KeroBlasterEn-v1063.bpm
https://www.cavestory.org/downloads/KeroBlasterEn-v1072.bpm
https://www.cavestory.org/downloads/KeroBlasterEn-v1400.bpm

To get an older version of Kero Blaster you need one of these patch files and a copy of English Kero Blaster v1.5.0.1a (current version as of writing) from either the Humble Store, Playism Store (from when it was still available), or GOG.com.

For GOG.com the installer you will need to copy the rsc_k folder, dxwebsetup.exe, KeroBlaster.exe, msvcp100.dll, msvcr100.dll, ReadmeEn.txt, vcredist_x64.exe, and vcredist_x86.exe into a new folder called KeroBlasterEn before starting.

Apply the .bpm patch to the KeroBlasterEn folder using beat patcher, which you can get from http://www.romhacking.net/utilities/893/ or https://www.cavestory.org/downloads/beat_patcher_v01.7z

To do this:
1. Open beat patcher.
2. Click "apply patch".
3. Select the .bpm patch.
4. Select the KeroBlasterEn folder.
5. Create a new folder to save the patched folder contents to and select it.