Exposing globals as read-only

Consider a problem of exposing some
T foo;
for read-only access by other modules, in order to prevent inadvertent 
(as opposed to malicious) writes to it. I cannot afford and/or do not 
want to incur the overhead of access functions. A solution could be:

foo.h:
extern T foo;
#define foo ((const T)foo) //hide the original foo

foo.c:
#include "foo.h"
#undef foo
T foo;

There can be variations on this theme avoiding the often deprecated 
#undef, like
foo.h:
extern T foo;
#ifndef OWNER_foo
#define foo ((const T)foo) //hide the original foo
#endif

foo.c:
#define OWNER_foo
#include "foo.h"
T foo;

What are NG's opinions on whether
- it looks right aesthetically
- it is a good idea to "overload" the identifier
- this can be a recommended practice (pattern) for a company's coding 
standard
- (probably OT) this can confuse popular or bundled code browsers, 
debuggers etc

--
Thank you,
Ark