[plt-scheme] Redefining function from scheme/base

I'd like to redefine real->decimal-string in a module, and provide the
redefinition to other modules, but I'm not sure how to do this.

I'm using the module language, with #lang scheme at the top, and I get
the "module: identifier is already imported in: real->decimal-string"
error when I try to redefine.

It looks liike real->decimal-string comes from the scheme/base module,
but I'm not explicitly requiring it... it's just automatically
included as part of the scheme language.  So how do I redefine this,
and once I succeed at doing this, how do the consumer modules choose
my redefinition over the base version?

Thanks,

Mark