Yes, you can.

However, customer support is only available for the latest version.
Note that if you use an older version, you will not be eligible for support.

Follow the procedure below to revert to an earlier version:
1. Uninstall the installed versions of VOCALOID6 Editor and VOCALOID6 voice banks.
2. Download and install an older version of VOCALOID6 Editor and VOCALOID6 voice banks using the following link:

VOCALOID 6.0.3 (Windows)
VOCALOID 6.0.3 (macOS)
VOCALOID 6.2.2 (Windows)
VOCALOID 6.2.2 (macOS)
VOCALOID6 Editor 6.3.2 (Windows)
VOCALOID6 Editor 6.3.2 (macOS)
VOCALOID 6.4.3 (Windows)
VOCALOID 6.4.3 (macOS)
VOCALOID6 Voicebank Fuiro 6.1 (Windows)
VOCALOID6 Voicebank Fuiro 6.1 (macOS)
VOCALOID6 Voicebank Po-uta 6.1 (Windows)
VOCALOID6 Voicebank Po-uta 6.1 (macOS)
VOCALOID6 Voicebank ZOLA Project 6.1 (Windows)
VOCALOID6 Voicebank ZOLA Project 6.1 (macOS)
The authorization information will remain on your computer even after you complete the procedure above.
If you have already activated VOCALOID6, you can use it immediately without performing authorization after reverting the app to the previous version.

Note: For the installers of the previous version of the licensee's voice bank, please contact the applicable companies.