Certain articles are what they term subordinate provisions, and yes these can be changed somewhat easier and quicker than others.
The amendment order would need to be laid before both houses for 28 days. except for changing the date for commencement (Article 1(3)) which can be laid before either house for 28 days.
They used this to amend the order when the date was changed from April to October.
See Statutory Instrument 2006 No. 484 The Regulatory Reform (Fire Safety) Subordinate Provisions Order 2006:
2. In article 1(3) of the Regulatory Reform (Fire Safety) Order 2005 for "1st April 2006" substitute "1st October 2006".
If that article was not a subordinate provision it could not have been so easily amended.
When you dig a bit deeper there are some interesting articles that could also be easily changed
e.g. Artcile 9(7) the precribed information that must be recorded after a risk assessment is a subordinate provision,
so is article 25 Enforcement authorities....so the responsibilities for enforcement could also be changed.........give it to EHOs for example!!