Suppose you tell someone you are going to do something for them.  Then they do something which, had you known about it at the time, you never would have made the pledge/offer.

Is an honorable man bound to keep the pledge.

Or can he renege based on the new knowledge?

I suppose it depends upon how much of a pledge it was.  For example, if an honorable man makes a pledge (vow) to a woman in marriage, it really doesn't matter what she does in the future.  An honorable man is still bound to keep that pledge.

On the other hand, if you happen to tell someone you'll give them $1,000.00 to pay off a debt, and the person immediately spends $1,000.00 on something else and doubles his debt, I don't think you are necessarily bound to give that first $1,000.00 to him.  It really depends on the way the "pledge" was made.  For example, if he came to you asking for help to pay off a debt and you tell him you will help, then I would not hold myself to be bound since it now appears he really just wanted the $1,000.00 to pay for the new item he couldn't afford and it was really just a con-job.  

If there was a "friendship" of sorts, that friendship is likely to be over, but such a person probably isn't really a friend anyway.

I'm clearly not a man, but I agree with what TKGS said.  

I do think that the specific details of your situation matter.  Perhaps you can shed more light on them?

Our chapel has a set of rose vestments that the priest didn't like, so on Gaudete Sunday, he ended up wearing purple instead.  So after Mass, I offered to donate $1,500 towards a new set of rose vestments.  He accepted.  The next day, an announcement was made regarding an ecuмenical activity the church would be engaged in.  Had I known about that activity, I would not have made the offer.  But as it stands, the offer has been made and accepted.  
What would John Wayne do?  I know this is not a matter of sin/non-sin, but honor is the next most important thing to me.  If a man doesn't have that, he doesn't have much.  Would reneging now impact my honor?

Our chapel has a set of rose vestments that the priest didn't like, so on Gaudete Sunday, he ended up wearing purple instead.  So after Mass, I offered to donate $1,500 towards a new set of rose vestments.  He accepted.  The next day, an announcement was made regarding an ecuмenical activity the church would be engaged in.  Had I known about that activity, I would not have made the offer.  But as it stands, the offer has been made and accepted.  
What would John Wayne do?  I know this is not a matter of sin/non-sin, but honor is the next most important thing to me.  If a man doesn't have that, he doesn't have much.  Would reneging now impact my honor?

No.  An honorable Catholic would, upon realizing that this is not a Catholic Church, depart and never show his face there again.  Donating money to a non-Catholic sect is not something a Catholic should do.

Oh, and you should explain to the person (I presume the priest) that you will never participate in his evil.

But, seriously, when you're part of the Novus Ordo sect, what on earth did you expect?

The priest didn't wear the rose vestments on Guadete Sunday because he didn't like them?  

He said they were salmon colored, so he didn't wear them.

He said they were salmon colored, so he didn't wear them.

That's funny. My old priest in the SSPX also refused to wear the Rose vestments. The reason he gave was because they were the wrong color. He said they were pink and not rose. To him they were supposed to be "salmon colored."

Considering that the liturgical color is actually a choice on that day, the priest is within his rights to wear violet

Considering that the liturgical color is actually a choice on that day, the priest is within his rights to wear violet

Ah, you beat me to it.  That is my recollection as well.