What you need is OpenType glyph substitutions, which FontCreator doesn’t currently support. You can create all of the glyphs that you need then add the OpenType tables using another application.
Ask again here if you don’t follow, but its beyond the scope of support for FontCreator. VOLT can also be used, but I found the method used in that tutorial thread is easier.
Anyone using your font will also need an application that supports OpenType such as InDesign or Word 2010.
Another route is to use Autocorrect to replace whole words without using OpenType at all. For example if n+e = № then autocorrect would have to replace “done” with “do№” and “next” with “№xt” etc.