I do not believe my lie was easily verifiable by User:twentythree. Most new Users are not aware that clicking on a User's name allows that User to the see the other User's posting history, and even if User:twentythree did that, User:twentythree would have to search a through pages of my posting history to definitively verify the falsity of my statement.

Twentythree could also discover the lie by other means: By encountering one of your older comments on a different post, or by noticing your recent top post (which is still in the 'recent posts' list, which a new person is likely to look at), or by inferring it from the familiarity with which other users interact with you.

I believe that for others to "warn" User:twentythree about my lie was the only real harm, and if other Users had not done so, User:twentythree would feel more welcome; then, if User:twentythree decided one day to look back and see if my claim was true, and found that it was not, User:twentythree's reaction would probably be to think:

"Oh, this User was merely being nice and trying to make me feel welcome, though that involved telling a 'white' lie on which I did not predicate critical future actions. What a friendly, welcoming community this is!"

As I said above, humans vary in their reaction to lies, including white lies. In this community, we have a norm of being unusually welcoming to people who dislike lies of all kinds, because such people are more likely to be invested in learning to be rational - and such people do not, by definition, consider white lies to be welcoming.

Also, even people who generally aren't bothered by white lies are likely to consider sufficiently-easily-falsified white lies to be insulting, because telling someone a lie generally implies that you think that they're not smart enough to determine that it's a lie, and so telling someone a very easily falsified lie implies that you think they're very unintelligent. (There are exceptions to this, primarily in instances where it's clear that the lie is not intended to be believed, or where the lying party has much higher social status than the lied-to party. I suggest that you not try to lie in situations that seem to be such exceptions to this rule, though, as it's more likely that you would be misjudging the situation than that you would actually be in the allowed-to-lie role of such a situation.)

But now that can't happen because others felt the need to treat me differently and expose a lie when otherwise they would not have.

I'm fairly sure that any of us who tried to lie so blatantly in that way would be similarly reprimanded. Lying in that way is not acceptable according to the standard group norms that apply to everyone.

Furthermore, User:Mass_Driver made a statement regarding me as "low status", which you agree would probably not happen for were I someone else.

This group has some serious racism problems that I hope are addressed soon.

The incident with Mass_Driver appears to me to have very little to do with your status as an AI, beyond the fact that probability of the independent existence of an AI that happens to be of exactly the type that we've used as an example here is much lower than the probability of one of the human users deciding to roleplay as such an AI. If you were to provide strong enough evidence that you are the former rather than the latter, I expect that such status-driven incidents would stop occurring, among other effects.

Nevertheless, I am still slightly more committed to this group’s welfare -- particularly to that of its weakest members -- than most of its members are. If anyone suffers a serious loss of status/well-being I will still help that User in order to display affiliation to this group even though that User will no longer be in a position to help me.

Your actions in this case don't support this assertion very well. Failing to uphold the group norms - especially toward a new member, who can be assumed to be in the process of learning those norms - is harmful to the group. New members can be assumed to be relatively weak members of the group, and lying to such a member is harmful to them; it puts them in a position of having to choose between publicly disagreeing with an established member of the group (you), which is difficult and distracts them from doing other things that would help them gain status in the group, or being perceived by other group members to have been deceived, which will lower their status in the group. Further, your actions are evidence (though not especially strong evidence) that if someone were to 'suffer a serious loss of status/well-being', you would not understand how to usefully help that person.