aosp – How to update a self built LineageOS without redownloading/rebuilding all the sources?

I have been able to successfully build LineageOS 17.1 for my (unsupported officially) smartphone and I have self signed the build one month ago.
I would like to rebuild it with this month’s new updates, without having to redownload/rebuild everything that had not been changed.
To build it I did:

repo init -u git://github.com/LineageOS/android.git -b lineage-17.1
created .repo/local_manifests/roomservice.xml with all the device specific code
repo sync
Extracted the proprietary blobs
launched lunch to set up my device
make -j8 bacon
mka target-files-package otatools
signed the zip

What should I do to avoid fully redownloading and rebuilding everything? Is it enough running repo sync, mka target-files-package otatools and signing the new zip? Is there something I should do to clean up from the previous build?