It is important to note that frozen water is not a feature of FSX or P3D. When you see frozen ponds or lakes, you are seeing that because of the add-on scenery that features that. In RTMM's case, we are talking scenery like ORBX regions (e.g. Southern Alaska). It is important to not that ORBX initially designed their freezing water capabilities around FSX. When P3D came on the scene, the anomaly that ORBX used to create freezing water was a bit compromised. As a result, there are many of us who fly with the freezing water option off due to some unwanted side effects.
Making your own pond that freezes in the winter and is open water in the summer is doable given the right scenery development tools, custom textures and significant scenery development experience. Do you have that kind of experience?
If not, I would go with Jeff's advice.
Rod