NAT and ICMP

I have a firewall/router using nft.  It connects to the outside world 
with a single globally routeable IP address ('Real-IP').

I want to use the Real-IP both for NAT and for the firewall/router itself.

My understanding is that for tcp and udp:

   * for private source IPs, I can configure SNAT to use one port
     range, say 16384:65535.

   * and I can, elsewhere, configure the firewall/router to use a
     different range, say 0.16383, with no NAT required (inbound
     or outbound).

But for ICMP queries, I cannot find equivalent settings to manage the 
"Query Identifier".

It has occurred to me that the trick might be to SNAT all outbound ICMP 
queries, something like:

   .... ip protocol ICMP ip saddr 203.0.113.1 snat to 203.0.113.1
   .... ip protocol ICMP ip saddr 10.0.0.0/8  snat to 203.0.113.1

where 203.0.113.1 is the Real-IP. I'm guessing NATing the source address 
to itself is OK... yes ?

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Separately: where should I look to find the degree of conformance to the 
various "NAT Behavioural Requirements": RFCs 4787, 5382, 5508 and 7857 ?

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Thanks,

Chris