Why I can not access ISP mode again?

[lpcware]

Content originally posted in LPCWare by allankliu on Sat Dec 14 02:49:27 MST 2013
I have a mini board for LPC812M101JD20 (SO20, but not FD20). The attached PDF is its schematics. In this schematics, CP2102 was used as USB/UART bridge, two buttons (ISP/RST) are used to enter ISP mode to download the hex code via Flash magic software.

Currently I haven't populate onboard CP2102, but using an external PL2303. And I didn't populate 12MHz crystal as well, since I think IRC will be used during ISP anyway.

By pressing and releasing RST while holding ISP key, I can enter ISP mode and program hex code. However I can not enter ISP mode later with same actions.

Do I miss anything to enter ISP mode again?

Looking for quick suggestions, since I have already put them on production plan. I am going to use it as a mini-dev-kit for Android USB host application.

[lpcware]

Content originally posted in LPCWare by TheFallGuy on Mon Dec 16 02:13:02 MST 2013
The ROM Bootloader is in ROM...  it cannot be changed.

[lpcware]

Content originally posted in LPCWare by allankliu on Sun Dec 15 21:51:11 MST 2013
Since silicon 4C, NXP changes ISP pin from P0_1 to P0_12. I have no idea why they change it? The blank chip drops into bootloader mode, so I can entern ISP anyway. But later on, since they changed PIN, I can not enter ISP with P0_1. But it works with P0_12 anyway.

Is there any way I can downgrade bootloader from v13.4 to v13.2? By flash magic?