EDITS 09302016:  model bugfix (trailing delimiter).  updated pics
I was working on a model where I needed to split a string up, change a part, then join it back together. Problem was that even though there's a Split operator, there wasn't a Join operator, so here's a homebrew op.
Like any Join operator, you can specify a delimiter to separate parts. Unlike others, however, this one is limited to joining 15 elements because that's about all I needed. This model has a chain of repeating parts, so if you need to handle larger joins, just copy-paste that repeating part to heart's content. I recommend inserting new parts into the second to last position. Mind the indexes. Here's what it looks like under the hood: