R6RS specifies exported variables are immutable.  I think it is natural that this immutability is also shared by aliased identifier, e.g. if you say as follows, 'x' should become immutable as well:

  (library (foo)
    (import (srfi :212))
    (export y)
    (define x 10)
    (alias y x))

Should it be mentioned in the srfi doc?

--shiro