I have noticed that こんにちわ and こんにちは can be spelled differently and have the same meaning. Does this occur with any other character combinations at the end of words?
No, the vast majority of word-end わ are not interchangeable with は.
A few words contain は read as わ (wa) as part of the word.
- こんにちは ("hello"; read as こんにちわ)
- こんばんは ("good evening"; read as こんばんわ)
- では ("now", "so", "then"; read as でわ)
- それでは ("now", "so", "then"; read as それでわ)
- ならでは ("unique to ～", "only found in ～"; read as ならでわ)
They are spelled as such because these ～は are etymologically the topic particle は. In formal and proper writings, these must be written as ～は. For example, see: Why is konnichiwa spelt こんにちは?
In casual writings, however, some young people find it cute (or cool, friendly, or whatever) to write them as ～わ, as they are actually pronounced. It's like English speakers spelling "you" as "u"; everyone knows it's wrong but can't help doing so because it looks somewhat nice in certain situations. Keep in mind they are absolutely inappropriate in formal writings, and do it only when you know what you are doing.
Of course there are also many words that end with は and read as ～は ("ha").
こんばんは/こんばんわ is the only case I am aware of that shares this distinction, but I think using は is probably more common. It's more "correct," at least, though people will probably call me a terrible prescriptive grammarian for saying that.
EDIT: I didn't mention this earlier because I thought you could infer it, but just in case: The reason they are interchangeable in these contexts is because は is being used as the topic marker particle here, where it is normally pronounced わ. So it's not strictly part of the word.