socat filter and replace character for modbus ascii

The goal is to get modbus ascii working with a Wallbox from ABL. So I placed a RS485 to TCP converter in the box, created a pseudo tty for my application and got the wrong frame. The answer starts with > and should start with :. So my approach is the following:

Terminal1: sudo socat -d -d -d pty,link=/dev/ttyVA00,echo=0,perm=0777 pty,link=/dev/ttyVB00,echo=0,perm=0777

Terminal2: sudo socat -d -d -d pty,link=/dev/ttyV0,perm=0777 tcp:10.10.49.249:502

Terminal3: cat /dev/ttyVB00 > /dev/ttyV0

Terminal4: cat /:/g' > /dev/ttyVB00
           
Terminal5: ./modpoll -m ascii /dev/ttyVA00 -b 38400 -d 8 -p even -t4 -c 2 -0

And this works! Could you give advice on how to simplify the socat solution and how to get it to autostart?