Calin,
A few details:
I am assuming you are putting a space before the "br #0123h" so it is properly considered as a mnemonic, right?
If you don't have any label that references the assembly piece of code you just wrote, chances are the linker will automatically remove it (it is not called from anywhere). In this case, you could try to define a symbol and call it from your C source code.
.sect .blentry .global my_func .asmfunc my_func br #0123h .endasmfunc
Not all details are accurate, therefore you should take a look at section 6.5 of the MSP Compiler User's Guide (a link to it is here)
I am unsure how the symbol _c_int00 would be called, but the section I referenced above mentions the & operand to access variables, therefore you could try the same with functions.
Hope this helps,
Rafael