i fear you may be suffering from a common misconception about "unstable", because Liquorix uses that in its changelog file. Are you just going by this, or have you actually tried it and found problems with it?
Debian provides built-in tools that you can use to rebuild any package in the repos, and there are many tutorials for doing that. I will let you find them as part of a learning experience instead of spoon feeding you the answers.
Hints: they would involve the "deb-src" lines in your sources, "apt-get source linux-image-$(uname -r)", "apt-get build" and so on. The 1000Hz kernel context switch setting can be accomplished by editing /debian/config/config, currently starting at line 5949:
Code: Select all
##
## file: kernel/Kconfig.hz
##
## choice: Timer frequency
# CONFIG_HZ_100 is not set
CONFIG_HZ_250=y
# CONFIG_HZ_300 is not set
# CONFIG_HZ_1000 is not set
## end choice
It's rather obvious to me what you need to change, but ask if you're not sure.
You probably just want a small increment at the end of the version for your new or modified stanza in the debian/changelog file, so that the next Debian security update will want to upgrade over your modified kernel, and alert you that you need to repeat the procedure with the updated source, so that you can keep up with the security fixes. The current version ends with "deb9u3", so just make it "deb9u3+1000hz" or something. Then "deb9u4" will still upgrade over it. If you want to prevent any upgrades, add or increment an "epoch" to the beginning of the version, as in version "1:4.9.30-2+deb9u3". This means it's up to you to watch for any Debian security updates.
Note that a Debian kernel package rebuild takes several times as long as a generic or Liquorix kernel rebuild, mostly because of the creation of the docs package. Also allow about 20 GB of free space on the drive for the build procedure.
Once you've done this, maybe you could try building and hosting your modified kernel on the openSUSE build service, which can build Debian packages from the source and automatically set up a repository for them. Besides doing all the work of building the kernel for you, this will also allow you to share it with others.
Edit: just saw dasein's response--has anyone else suggested the built-in tools?