RFC2821bis-01 Issue 4: Client actions on receipt of 4yz and 5yz codes

In RFC 2821bis-01, Section 4.2.1 (Reply Code Severities and 
Theory), in the description of the generic 4yz category, 
described the desired action in terms of what the client "is 
encouraged to" do.  I was persuaded in an off-list exchange that 
this can reasonably be changed to "SHOULD" and -01 reflects that 
change.   For 5yz, there was a similar construction that 
indicates that the client "is discouraged from" repeating the 
request.  I was less confident about changing that to "SHOULD 
NOT", so the "is discouraged" text remains in -01.
Question: Should the 5yz description  be changed to use "SHOULD 
NOT".   If not, is "SHOULD" in the 4yz description reasonable?
     john