I suggested this awhile back in 2019.
https://www.spigotmc.org/resources/knockback-editor-1-7-1-8.40767/
This plugin allows you to change in-game velocity. It currently only supports 1.7 through 1.8, but I don't see any point in any servers with versions greater or equal to 1.9 would use this plugin.
Fun fact: skript can’t do this properly. You could register the custom event with skellett (because on knockback isn’t a valid event) but you HAVE to put a delay when using skript so the kb would be delayed.
or https://www.spigotmc.org/resources/knockback-changer-with-config-file.91588/ idc we really need a kb changer ples