--Good news! I'm not going to have surgery after all. The do

不行,could表达的是比can更委婉更礼貌的请求,换了语气都变了

不行，这里是虚拟语气，应当用could这种过去时态

yes
--Good news! I'm not going to have surgery after all. The doctor says I can start working out again soon and maybe play football like before in a few weeks.
--That’s terrific! It will be great if you could（这里could可以改为can吗？） get back in shape in time for the World Cup.