How to make a text multiplechoice from a text formula field

I think that you are asking how you can make those choices be a drop down and not have to be perfectly typed in.

You can't.

So Plan B is to either name a field [Enter SP or GP] and use that on your form (ie  make it a mirror field to your formula field,  with a formula of [My formula field]

I know that is not what you want.

My real suggestion is that I personally despise <ask the user> reports, so I try to have a report that lists all relevant records and then make the first Dynamic Filter be that choice for the user to filter the report after it runs.

 

I'm saying that I do not think it is possible to make the <ask the user> be a drop down field when it is a formula field.  

So we move on to Plan B is to how to get your users to hand type either SP or GP in the box.  ie how do we put up some help text on that <ask the user screen> they hit.  Well there is not a way to put help text on that screen,

so we move to Plan C

Make a new formula field called

[Enter SP or GP]

make the formula just refer to your formula field that you already have.  The only purpose of a duplicate fild is to give you a way to make a wordy field name like

[Please input SP  for SP projects or GP for GP projects]

That way when the <ask the user> comes up there will be an explanation to the user.  ie change your report to <ask the user> on this mirror field. and not the real formula field - just so that the <ask the user> experience has "help text".

I�m not understanding how you used form rules to solve a problem when running a report. Maybe you put the report as an embedded report on a form?