What the contract is correctly saying is that there can not be an instruction issued to change anything in Contract Data - like you say change Delay Damages form £10/day to £1000/day.
When it comes to compensation events - these can obviously affect planned Completion and thus Completion Date. If you look at the definition of Completion Date, it states that it is the date stated in the contract data unless changed in accordance with the contract. The contract states that implemented compensation events can move it later,, and acceleration once agreed can bring the date earlier. This now contractually supersedes the date stated in contract data. There is no requirement to physically go back into contract data and change the date there.
When it comes to compensation events - these can obviously affect planned Completion and thus Completion Date. If you look at the definition of Completion Date, it states that it is the date stated in the contract data unless changed in accordance with the contract. The contract states that implemented compensation events can move it later,, and acceleration once agreed can bring the date earlier. This now contractually supersedes the date stated in contract data. There is no requirement to physically go back into contract data and change the date there.