Restrictive Rules and regulations

Tenancy Types and Management

I am having increasing difficulty with the Management Company of a block in which I own and let a flat. I have owned the flat for about 18 months, in addition to the Lease there is an extensive list of rules and regulations that make it more like living in a police state than a residential block. My tenants do there best to abide by the rules but it is becoming increasingly difficult.
Following a recent AGM the rules and regulations have now been changed and made even more dracoanian and I am being asked to sign a copy. I have particular concern that they are now insisting that when the tenant changes I use one of 2 letting agents they prescribe and that those agents are then employed to manage the letting.
Neither of these agents are one that I would normally use and I manage the property myself, not only to save cost but because I find it better to have a close personal relationship with the tenant and it seems to work. Can I be required to sign rules and regs that have been amended after I purchased the property and is it reasonable or even enforceable for them to demand I use the agents they prescribe and to pay them to manage it which i have been doing very well myself.