caciara, the procedure is optional - if you are not happy to use it for any reason, then don't use it. Obviously this may mean that your approach colleagues may need to increase the spacing between inbounds.
Whether it is 'legal' depends entirely your national law framework. Nothing in the ICAO Annexes/PANS is law in your country until it is transposed into your legislation. If the land after/RRSM procedures are in your law then to do something different, even if the ICAO SARP on which the law is based changes, is probably unwise. If the procedures are in a manual published by your CAA - as CAP 493 is - then I would expect them to have a reason for not updating it (even if it's not obvious to you), that's their job. Again, doing something different is probably unwise.
Fortunately with this procedure you can choose whether or not to apply it. Things might be different if there are no alternatives available to you.
I'm not operational any more but if I were in your position I would personally - in principle - be happy to apply the national procedures in CAP 493. However, the fact that the procedures are confused/confusing and do not accord with the current ICAO procedures seems unnecessary and undesirable.
Maybe the EASA rules will solve these problems....