Change of accounting date for LLP - basis period abolition

Apologies if this has already been queried elsewhere or if it should be in a different forum. I have an LLP client that wishes to extend their accounting date to 31 March 2024 to bring it in line with the tax year end and the abolition of the basis period rules. This is financially more viable for them owing to the additional costs that would arise should they continue with their current 31 December year end. However, they last extended their accounting period end-date to 31 December 2021 when they incorporated into an LLP, so less than 5 years ago. It is my understanding from reading various guidance available that although the law has not changed in respect of extending the accounting period end date within 5 years, i.e. it must be for a commercial reason, it would be accepted that the abolition of the basis period is a commercial reason. How exactly should this be reflect on form LLAAA01? Or, does separate authorisation from companies house still need to be sought in order for the change of accounting date to be accepted?

Hi Emily Watts,
The first thing to say here is that the LLP itself does not have a basis period, rather it is the individual partners in the LLP (those subject to IT not CT) that will be subject to the basis period rules and therefore be affected by basis period reform in respect of their notional business as a partner in the LLP.
The LLP itself produces accounts and has an accounting date and so under the old basis period rules it was any change in the LLP accounting date that needed to meet the relevant criteria as per (BIM81045 - Computation of liability: basis periods - change of accounting date in year 4 onwards) in order to be effective to change the partners basis period in the year of change of accounts.
However, for 2023-24 onwards the rules will be relaxed as we move through the 2023-24 transitional year into the new tax year basis of assessment from 2024-25. 
Here is a gov.uk link that gives some basic details of the changes on moving to the new tax year basis and contains a para that talks about changing accounting date in 2023-24 and the restrictions not applying from then (they still apply for years up to and including 2022-23)  How HMRC assesses profits for some sole traders and partnerships to change (How HMRC assesses profits for some sole traders and partnerships to change).
The guidance in the Business Income Manual for the new Tax year basis and the transitional year is at BIM81200.
For continuing trades started prior to 2023-24 the guidance at (BIM81260 - Transitional rules: basis period components for continuing trades) onwards covers the components of the partners basis period for 2023-24 and how this is calculated.
As regards the notification of a change of accounting date to Companies House on form LLAAA01, I suggest that you should contact companies house for guidance on completion of this, as it is only LLP's/LP's that this is likely to effect as sole traders and ordinary partnerships do not have to send accounts to companies house.
Thank you.