Yikes!!!!
NO ETCHING!!!
This is not my opinion, but the facts as told by a paint manufacturer. If you do not want to believe me do what I did, call them and ask.
It is an acid layer and technically only for virgin metal, not for rust prevention.
More important is it will be a source of epoxy failure. The acid will prevent the bonding layer from curing. Keep in mind the agent that causes the epoxy to cure is a base.
Read the directions. I know PPG and SPI will tell you 2 coats direct to metal. SPI will tell you do not use any acid products first (BTW it is the owner of SPI that explained to me about the how and why). Then you must put the next coat during the recoat window of the epoxy. I believe it is 7 days for SPI and 3 for PPG, but I could be wrong. The epoxy must be kept above 60 degrees for like 24 hours (again check the directions). If it is allowed to cross below a key temp it stops curing and will not restart when it warms up (learned from the owner of SPI).