If the following is a more detailed response than what you had in mind, I apologise in advance.
“Does a colon always end a sentence?”
This is actually a technically fraught question about what is meant by ending a sentence. Arguably, colons and semicolons never end a sentence. To explain: going back to my school-day’s in the early sixties, before their use started to diminish in favour of simplicity, I was taught that they were to be used for breaking up sentences into manageable chunks; Victorian writers like Dickens, were lauded for both their love of long descriptive sentences with multiple clauses and their skilled use of colons and semicolons to make these sentences readable.
These days, although verbose prose is unfashionable, colons and semicolons are still useful; even though their use comes at the expense of increasing the average length of a sentence.
Some hard rules about the use of colons and semicolons from which we can derive possible patterns.
After a quick bit of research I found this page from the University of Leicester student guide http://www2.le.ac.uk/offices/ld/resources/writing/grammar/grammar-guides/semicolon
Which, with some additions, I summarise as follows:
To separate items in a list
To link sentences which are closely related, [linking two independent clauses.]
For use with otherwise, however, therefore…
To introduce a list
To introduce an explanation, conclusion or amplification
From the 1st link below: the colon is used to link an independent clause with a quotation
From the 3rd link below: to separate two independent clauses that are directly related.
Note: The choice between using a colon or a semicolon to link two independent clauses is decided on the basis of whether the clauses are either directly or indirectly related.
A deeper explanation of the use of the colon and semicolon can be found at the following:
(Note: Because of a slow internet connection, for the moment, I'm having problems downloading Ratel, but that's my problem.)
I have downloaded the segment.srx file and am currently studying it in Notepad++. This has allowed me to identify the appropriate section and get a rough feel for the basic rules, along with how they are organised.
The first, (or biggest,) problem that I can see with simply redefining “SENT_END” would be what it would do to higher level rules; in particular capitalisation, though there are probably other rules that would be affected.
Whether to capitalize after a colon is by and large a matter of personal taste, a quick internet search shows little formal agreement among authoritative sources: Some people argue that in British English, only proper nouns are capitalised; however, I am a UK educated Scot who, (possibly as a result of American text-books,) has always tended to capitalise the first letter of an independent clause following a colon.
On the other hand, except in the case of proper nouns, one never capitalises after the semicolon.
(See here http://data.grammarbook.com/blog/semicolons/semicolons/ )
As I said, I apologise if you feel I have gone into too much depth, but, if you are not offended, I look forward to hearing your thoughts on how to proceed.
By the way, where exactly would I find the "forty word rule" in the open office add-on? I have been looking through the directory and can't see it, similarly it does not appear to be in the grammar.xml file.