Wouldn't that risk resulting in double-slows, if you, say, would be hit by the home-made slow while standing in Oil?
You can avoid double Slowed if you use the same Stack ID as the original Slow - that way only one can be applied at the same time. You can even customize your slow by making it have a different Stats ID, which would allow you to change how much it slows them. If you use the same Stats ID as the original Slowed, you'll retain the same stat changes.
data "StatsId" "Stats_Slowed"
data "StackId" "Stack_Slowed"
StatsId entries are located in the Potion table by the way.
