No, an agent may NOT alter your offer after you put it in without your concurrence or consent; obviously, they can recommend to you that it be changed, but that's all they can do--recommend. You could sue the broker/agent for professional malpractice; if you can sue show that their alteration cost you the property, you can potentially recover your losses, such as the lost profit, but bear in mind that proving potential or future profit can be difficult, and is subject to offsets or reductions, such as for the time cost of money ("reduction to present value"), a discount for risk (no investment is certain), etc. Thus, you have a reasonable chance, based on what you write, of recovering something, but it may not be as much as you think or hope it will be.