In terms of whether they can change your role when on maternity leave, it partly depends to what extent has it changed and what is the reason for the change. Do you know either of those?
Also, bear in mind that if you've taken longer than 6 months off, they are not obliged to give you the same job back anyway, if that's not practicable, they have to give you one that is suitable on same terms and conditions.
When you put in your request to reduce to 3 days a week plus the 3 extra days a month, how were you proposing that was to be achieved? Did you think your existing workload could be done in the hours you are suggesting or were you suggesting changes that would make it possible?
I have recently submitted an application to return to work 3 days a week; plus 3 flexible days a month instead of working full time (any 5 in 7), and had my meeting at work last week. During the meeting the manager kept sayuing I couldn't do this and that as my role had changed and the workload had increased and the support from other departments had diminished. I felt completely unprepared as non of this had been explained to me prior to the request being put in. I have left the application with them but anticipate it being rejected. Can they do this whilst I am ok maternity leave? Advice on my next move please