So you want to modify the ICA Client but you want to do it once and have it affect everybody.  Maybe you need to change the URL of your PNAgent site (in which case I'd just change the dns entry), I don't know your reasons but the answer is simple.  Use Group Policy and a special ADM which can be found here:

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<a href="http://support.citrix.com/article/CTX112957">http://support.citrix.com/article/CTX112957</a>

This is supported on versions 10 and above.  Good luck, your AD environment needs to be in good shape otherwise ADMs can bring more trouble than they are worth.