Заменить буквы в слове - Assembler

.386
.model flat,stdcall
option casemap:none
                        include C:\masm32\INCLUDE\WINDOWS.INC
                        include C:\masm32\INCLUDE\KERNEL32.INC 
                        include C:\masm32\INCLUDE\USER32.INC
                        includelib C:\masm32\lib\kernel32.lib                
                        includelib C:\masm32\lib\user32.lib
                        
.DATA
mes1 DB "makros",0
mes2 DB " '%s' ",0
titl DB "Info",0
buf DB 256 dup(0)
 
.CODE
START:
mov eax,offset mes1
mov byte ptr[eax+2],'3'
mov byte ptr[eax+4],'3'
 
invoke wsprintf,addr buf,addr mes2,eax
invoke MessageBox,0,addr buf,addr titl,0
invoke ExitProcess,0
END START