Can I install Android 4.2.1 AOKP IceColdJelly ROM on my HTC One X by AT&T? Can the Android 4.2.1 AOKP IceColdJelly ROM that seems to be released for the HTC One X international model be installed on HTC One X subscribed by AT&amp;T?

I found the update for HTC One X on following link :

Android 4.2.1 AOKP IceColdJelly ROM for HTC One X

Does my HTC One X from AT&amp;T support this ?
No you can't flash an international ROM on your device.
Because your phone's configuration is different than international version.
Details are given below:

Chipset: Qualcomm MSM8960 Snapdragon (AT&amp;T)-----  Nvidia Tegra 3 (International)
CPU:    Dual-core 1.5 GHz Krait (AT&amp;T)-----   Quad-core 1.5 GHz (International)
GPU:    Adreno 225 (AT&amp;T)---------               ULP GeForce (International)

if you flash this , it may brick your phone.

See this