should -> must

This is what I want the spec to say. But it's not backwards compatible.
Can we get away with this?

debug_module.adoc

@@ -369,11 +369,11 @@ of {dm-data0}) or hart (e.g. contents of a register modified by a Program Buffe
 Before starting an abstract command, a debugger must ensure that {dmcontrol-haltreq}, {dmcontrol-resumereq}, and {dmcontrol-ackhavereset} are all 0.
 
 While an abstract command is executing ({abstractcs-busy} in {dm-abstractcs} is high), a debugger must not change {hartsel}, and must not write 1 to {dmcontrol-haltreq}, {dmcontrol-resumereq}, {dmcontrol-ackhavereset}, {dmcontrol-setresethaltreq}, or {dmcontrol-clrresethaltreq}.
-The exception to this rule is when the debugger writes 0 to
-{dmcontrol-dmactive}. In that case {hartsel} may be written with a new value
-(which the hardware should ignore).
 The hardware should not rely on this debugger behavior, but should enforce it by
 ignoring writes to these bits while {abstractcs-busy} is high.
+The exception to this rule is when the debugger writes 0 to
+{dmcontrol-dmactive}. In that case the hardware must be unaffected by the new
+value of {hartsel}.
 
 If an abstract command does not complete in the expected time and
 appears to be hung, the debugger can try to reset the hart (using {dmcontrol-hartreset} or {dmcontrol-ndmreset}).