From what you say, you are on O2 LLU so do not go near the BT broadband equipment in the exchange. So the fact they are changing the BT equipment is totally irrelevant to your connection.
Can you confirm you are on O2 Standard, not O2 Access? Many people get confused about that, as both are "up to 8Mbps", so get incorrect advice from us.
See my What is LLU?
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