#define with space

You could do...

#define replace replacement
#define to here

Watch out for unintended side effects of the defines. You would probably want to #undef them after they've done their job.

no, you can't

#define identifier something

what you define must be an identifier which cannot contain space. Nor can it contain hyphen, begin with a number, etc. you can define only an identifier

what you wrote will work

#define replace to replacement here

but not as you expect. This line defined replace to be substituted with to replacement here