Halp! If you won't be....

It can, but it is rather awkward. Most native speakers would say:

"If you can't do the photo shoots, please let me know."

Thanks!

So in my own defense I presented it to my Better Half, whom almost everybody hereabout would agree is much smarter than I, and she found it perfectly normal

The OP phrasing is slightly more diplomatic and less confrontational.

There is a slight shade of meaning. I had not thought of that, so thank you.

The sentence quoted seems perfectly normal, but I have a problem with the word "halp" in the thread title. Perhaps others are more familiar with it than I. is it American jocular/informal for "help"?

Haha, I saw someone use it and learned it's same as 'help'.

halp/help

They're not the same in Canada or most English-speaking countries. It would be taken as a typo in Canada (or an indication of a non-native speaker).

Perhaps you could find out the origins of the person using it.

Absolutely. I too, thought it was a typo the first time I saw it. I looked it up and this is what I found on urbandictionary.com -

*****
HALP
1) Help.

2) Favorite word of Code Zero, used when he is in distress.
1) HALP! How do I surf the net!?

2) Aarun: dood rawns not gona do bootz no moer
Code Zero: lol HALP!

An exaggerated form of help, usually used when in distress.

Can also be a chatspeak form of help.
"HALP! I tied mah legs together and I can't get them untied!"

"I not needs a halp"

A desperate way of saying help. Usually used in emergency situations where mispronunciation due to events occurs. Notorious for use in lolcat pictures.
Ex. Tom: ****! I'm drowning!

Bob: What do I do?!!

Tom: Halp!

*****
So... I tried to express that I desperately need help

I don't get this. Is there anything wrong with my post? Please let me know. Does my tone sound confrontational? English is not my first language so there could be something in my post that rubs you the wrong way. Honestly, I'm not here to confront anyone. I just want to ask questions, collect answers, and share them with other learners of English.

Not at all. Your original phrasing was as polite as any one could ask for. It was a subtle difference and only someone being hyper sensitive would be put off with the alternate phrasing that jes(?) suggested. It's just that I could imagine it being spoken with a hint of impatience.

Again, your original wording in your OP was not in the least bit confrontational.

Oh silly me, I get it.

urbandictionary might be fine for understanding things people say, but it's not terrific if you're trying to work with written English - it is non-standard and based on voting, not actual knowledge of language.

The other factor is that people make up words and post them in urbandictionary (along with their definitions). We have at least one A2k member who does that. I suspect he hasn't thought through the implications for EAL/EFL students.

Oh, ok I'll keep that in mind. So it's like someone like my 8-yr-old nephew goes on the Internet and makes a dictionary entry. We actually have that problem in Korea