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That was my fear, too, and the truth is you WILL lose clients. But those are not the clients you want, anyway. Figure out your ideal client and target them in your marketing.
Fewer clients, but more work and profit per client.

A great I heard it put recently is that for many of your existing clients, this new business model may be like trying to put square pegs in round holes, when what you'll end up doing with your marketing is attracting all the round pegs.