Whear is fasm out asm text ?

When Fasmw 1.73 work with EQU, macros, Text and replaced this, then how fasm out text?
I mean memory address Whear is I taked this text, changing and gived back fasm to continue compiling to code.

Idea write in fasm mechanism give User text.
User modified text(replaced User tokens, words) and gived back fasm to continue compile text to code.

Code:

b equ 5
c equ esi
Mov %usrreg, b
Mov %usrreg, c

Fasm get error undefined %usrreg.
If fasm gived this text User, or put in fasm compile pipeline User code.
Then %usrreg replaced eax(for example)
Next %usrreg replaced add ebx, eax and add c(esi) .
And after fasm continue compile text to code.

This gived User do more complicated and cool stuff, after macros and preprocessing done work.

User must gived fasm code for replacing.

Code:

;in User file
%usrreg2 (Inc eax) 
%usrreg ( eax;ebx;edi)
%usrmm (mov eax, esi\\call procA;call procB)

First %usrreg replaced eax
Second %usrreg replaced ebx
All %usrreg2 replaced Inc eax

First %usrmm replaced mov eax, esi and call procA
Second %usrmm replaced call procB