have+object+past participle

[Saneta]

1. My hair looks deadful; I think I will have it set tomorrow.
2. I'm afraid it's rather draughty here but I am having broken pane replaced tomorrow.

1.why not: My hair looks deadful; I think I am having it set tomorrow.?
can it be also like that?

2.can it be also: I'm afraid it's rather draughty here but I will have broken pane replaced tomorrow.?

Many thanks

[Dozy]

"I will have it set tomorrow" -- It is my intention to do that.
"I am having it set tomorrow" -- It has been arranged that this will happen. (So, "I think I am having..." means you think you have an appointment but can't remember for sure.)

Same for "I am having / will have the broken pane replaced tomorrow."