There is background information below.
The questions are:
How common are the sequences that use \u200D and \u200C (ZWJ/NJ)?
If the 200D and 200C are omitted, is the text still understandable?
If the 200D and 200C are omitted, can it change a valid word into a different valid word?
If so, how common does this happen?
The following extracts text from SLS 1134 that describes the use of ZWJ and ZWNJ. For reference, it also adds Unicode literal versions of the text.
The rakaransaya and yansaya are forms of conjunct letters
.
ක්රෙ = \u0D9A\u0DCA\u200D\u0DBB\u0DD9
ක්රෙ = \u0D9A\u0DCA\u0DBB\u0DD9
ක්යෝ = \u0D9A\u0DCA\u200D\u0DBA\u0DDD
ක්යෝ = \u0D9A\u0DCA\u0DBA\u0DDD
NOTES:
...
2. The yansaya and rakaransaya are required in normal Sinhala text. However, if for
some reason, it is desired not to use the rakaransaya or yansaya, the zwj should be
omitted.
කර්ම = \u0D9A\u0DBB\u0DCA\u200D\u0DB8
කර්ම = \u0D9A\u0DBB\u0DCA\u0DB8
ක්ෂේ = \u0D9A\u0DCA\u200D\u0DC2\u0DDA
ක්ෂේ = \u0D9A\u0DCA\u0DC2\u0DDA
න්ද්රා = \u0DB1\u0DCA\u200D\u0DAF\u0DCA\u200D\u0DBB\u0DCF
න්ද්රා = \u0DB1\u0DCA\u0DAF\u0DCA\u0DBB\u0DCF