I bought 126 acres about a year ago and would like to 'simulate' getting in and off the property which should be big enough to accommodate a grass strip. Is it possible to develop a grass strip in FSX using coordinates where there is no field to replace? (i.e. insert a brand new field)

Yes. Any afcad program will do it. (ADE, AFX, etc.) All you have to do is put a runway where and what size and direction you want, put a flatten or ground poly around it, name it, (name, city, state, country) and give it an IACO or IATA code so it will show up in the menu and on the gps.

Thanks! I'll give it a shot and see what I can come up with.

Don't forget to read the manual. It has an example of a very simple airfield.

... Is it possible to develop a grass strip in FSX using coordinates where there is no field to replace? (i.e. insert a brand new field)

Hello. You can even sow the grass field, as described here.  ...And then plant trees there around. Good luck to You