Many thanks for your patience. The issue here is that under Regulation 4(4) of TUPE any changes as a result of the transfer are automatically void, unless the employer can show they were in no way connected to the transfer or if they were necessary for an economic, technical or organisational reason (ETO reason) subject to employee agreement or the terms of the contract permitting the change.
Some employers may try and justify changes by arguing that they are needed due to harmonisation and therefore rely on an ETO reason. However, Government guidance and case law has restricted the application of harmonisation as a genuine reason to amend a person's terms of employment. Harmonisation will only be a valid reason if there is a change in the workforce and this must involve change in the numbers, or possibly functions, of the employees. In practice, relatively few contractual changes would involve such changes so harmonisation will rarely be used as a justifiable reason.
So you are risking these changes being automatically void because they would be connected to the transfer and will not be for an ETO reason. You can still propose the changes you wish to make and try to get his consent, however if he refuses it may be best to accept them as they are, otherwise it could give rise to a constructive dismissal claim, where he is forced to resign due to this.
I hope this has answered your query. I would be grateful if you could please take a second to leave a positive rating (3, 4 or 5 stars) as that is an important part of our process and recognises the time I have spent assisting you. If you need me to clarify anything before you go - please get back to me on here and I will assist further as best as I can. Thank you