Best custom hook for service enable / disable and file copy in data partition

when converting an image i would need to
disable mender-client.service (or not enable it)
copy some file in /data/mender and /usr/share/mender
and add one or tow new services files
what would be the best custom hook ?
I was thinking at USER_LOCAL_MODIFY_HOOK ?
what do you think ??
and where could I find in docker builder the right volume to get the new files I want to add into image from

I tried to add this config file :
preauth_config :

disable_mender_client_service() {
    log_info "disable mender-client.service."
    run_and_log_cmd "sudo rm -f work/rootfs/etc/systemd/system/"

copy_preauth_files() {
    log_info "copy preauth files"
    run_and_log_cmd "sudo mkdir -p work/rootfs/data/mender/preauth"
    run_and_log_cmd "sudo cp preauth/* work/rootfs/data/mender/preauth"

change_iddentity_script() {
    log_info "change identity script"
    run_and_log_cmd "sudo cp preauth/mender-device-identity work/rootfs/usr/share/mender/iddentity/"

enable_preauth_service() {
    log_info "copy and enable preauth.service"
    run_and_log_cmd "sudo cp preauth/preauth.service work/rootfs/etc/systemd/system/"
    run_and_log_cmd "sudo ln -sf /lib/systemd/system/preauth.service work/rootfs/etc/systemd/system/"

I call mender-convert with --config config/preaut_config
I well seen the use in log :

2021-04-16 12:15:57 [INFO] [mender-convert-modify] Using configuration file: configs/preauth_config

but when hook time is coming specific hook time nothing logged

2021-04-16 12:16:04 [INFO] [mender-convert-modify] Performing user/local specific modifications (if any)
2021-04-16 12:16:04 [INFO] [mender-convert-modify] Running hook: user_local_modify
2021-04-16 12:16:04 [INFO] [mender-convert-modify] Applying rootfs overlay: rootfs_overlay_hosted/
2021-04-16 12:16:04 [DEBUG] [mender-convert-modify] Running: (./mender-convert-modify:369): run_and_log_cmd():  

	sending incremental file list

sent 1,023 bytes  received 50 bytes  2,146.00 bytes/sec
total size is 846  speedup is 0.79

The variable name is plural: USER_LOCAL_MODIFY_HOOKS

how I could have missed that … sorry all my apologies