The USB Addon way didn't survive the 2nd boot, used a different entry point. With that it was possible make the OS2AHCI.ADD (community version), OS2APIC.PSD (ACP/WSeb) still be loaded in second boot (from C:\), It remains in the config.sys during 3rd, 4th reboot - so its final.
File and Print 2 ...

The first boot changes for AHCI, ACPI, USB-CDROM works, the installer sees AHCI disks, CD/DVD. Now I need to find the way to put these changes onto the harddrive before second boot. The changes I have made are dependent on USB option, so that need to be switched on & set up with files. Plan to move ...

Hi,
Thank you for the answer and the details, no problem.
I'm doing the UPDCD project (v2.61) in a dedicated VMWare VM, based on MCP2 - English version. I can share the VM or its key configs it if helps, it builds a working image. I use either FTP local LAN, or a USB pendrive to transit & test ISO ...

Hi Sigurd,

I was looking a way to add AHCI, USB CD/DVD into an UPDCD update MCP2 and based on other forums' topic you are the subject matter expert. The last posts I've found are from here:
Which config.sys does OS/2 use for the second stage of installation?
[Tutorial] [Projekttagebuch] OS/4 ...