Changes are IMHO easy to do.
Gui Guided
1.) F2 - Privacy and Security settings. Open droppdown menue. Chose Custom
2.) Tools -> User Agent chose. Choose Custom
3.) Part of the Privacy Bar. Right Click on user Agent. Choose Custom.
On "Custom" You can insert a new UserAgentString such as:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.18) Gecko K-Meleon/1.6.0 not Firefox/3.5
You can alternatively edit the default settings file directly: ./k-meleon/defaults/pref/I10n.js Line 15+
pref("kmeleon.privacy.useragent1.name", "Firefox 3.5");
pref("kmeleon.privacy.useragent1.string", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.16) Gecko/20101130 Firefox/3.5.16");
pref("kmeleon.privacy.useragent2.name", "SeaMonkey 2.0");
pref("kmeleon.privacy.useragent2.string", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.16) Gecko/20101123 SeaMonkey/2.0.11");
You can add for example:
pref("kmeleon.privacy.useragent3.name", "New 3rd custom string Opera bla bla");
pref("kmeleon.privacy.useragent3.string", "Opera/10.00 (Windows; U; Windows NT 5.1; en) Presto/2.2.0");
Alternatively You can go about:config (aka Edit/Configuration/Browser Configuration) and add new items from there.
I added for example:
Name: general.useragent.extra.K-Meleon
Type: string
Value: not Firefox/3.5
Else You can edit ./Your profile/prefs.js directly.
I personally use the default settings file and about:config to customize.