And one more:
When I read back the project SIL file it seems to overwrite translations I have made in the code using TsiLang Expert (design time) with blanks from the SIL file. Am I observing the behavior correctly and if so, can it be flagged to only read in non-blank entries?
No this can't be changed, loading- loads all content from SIL file and overwrites existing values/content. You can merge SIL files first in SIL Editor as you need and later load it into TsiLang.