yes you can disconnect the D2 BNCS connection and launch multiple MCP connections. 

Yes, there is enough public documentation to make a clientless bot in d2, still there is no yet a public clientless bot for d2.

The only thing i havn't seen public is the warden handler for d2, you will just be able to stay in the game for 60 seconds before getting droped by the server if you dont answer to this packet correctly.

There are 3 binary protocols you need to emulate to do so:
- BNCS (Battle.net Client to Server)
- MCP (Master Control Program, aka Realm)
- D2GS (Diablo 2 Game server)

You can find information about the BNCS and MCP packets in here:
http://www.bnetdocs.org/

BNCS Login Sequence:

C > S [0x50] SID_AUTH_INFO
S > C [0x25] SID_PING
S > C [0x50] SID_AUTH_INFO
C > S [0x25] SID_PING (Optional)
C > S [0x51] SID_AUTH_CHECK
S > C [0x51] SID_AUTH_CHECK
C > S [0x3A] SID_LOGONRESPONSE2
S > C [0x3A] SID_LOGONRESPONSE2
C > S [0x14] SID_UDPPINGRESPONSE (Optional)
C > S [0x0A] SID_ENTERCHAT
S > C [0x0A] SID_ENTERCHAT

MCP Login sequence:
http://forum.valhallalegends.com/index.php?topic=11383.0

You can find a D2GS research by Ringo here:
http://forum.valhallalegends.com/index.php?topic=11756.0

I would recommend you to use MBNCSUtil if you want to give it a try on this.

The MBNCSUtil namespace provides managed types for the implementation of Battle.net logon authorization as well as a number of other utilities to support Battle.net development.   

http://www.jinxbot.net/mbncsutil/