mov [putchr_dat-4],eax
...
  mov al,[ebx+12345678]
putchr_dat:
    

Name = 4    

struc MyStruc {
  .field1  dd ?
  .field2  dd ?
}    

Simply learn and actively use the named constants...

Code:

Name = 4    

...and data structures:

Code:

struc MyStruc {
  .field1  dd ?
  .field2  dd ?
}    

Sometimes it goes usually that we change a number in the code so that

   mov [offset_var], eax
  ...
   mov eax, [offset_var] ; offset_var is in DATA section
   ; or in stack, in this case use addressing from esp/ebp
   mov al, [ebx + eax]
    

Quote:

Sometimes it goes usually that we change a number in the code so that

In this code you can use eax, because it will be modified anyway by the second mov command (if you don't use ah, of course).
In general you should not modify your code in run-time, because memory containing code should be write-protected for security reasons. It's MUCH better to use different register and/or variables to store needed offsets:

Code:

   mov [offset_var], eax
  ...
   mov eax, [offset_var] ; offset_var is in DATA section
   ; or in stack, in this case use addressing from esp/ebp
   mov al, [ebx + eax]
    

In this case you can reserve one register for storing offset or load the offset from variable every time. Modifying code in run-rime is very bad practice.
Also it can be possible to store direct address in ebx without need to add anything every time.

shr
    ecx,
  a:?    

push ecx
mov cl,[a]
shr dword[ecx],cl
pop ecx