Hebrew to English Tech/Engineering Engineering (general) Elevator Specs - Construction

The context:
"באם ידרשו שינויים או לא הגישו תוכניות בזמן הנדרש לפי סעיף 1.5 ויהיה צורך בהריסות ובנייה , תבוצע
עבודה זו ע"י המבצע ועל חשבונו."

Before I get lynched....I'm fully aware of the one term per question rule, but the problem here is that I understand each and every word of the clause, just not how they fit together or make sense within the sentence as a whole.

I believe someone is trying to tell me I shouldn't be working on Shabbat.
I'll be grateful for any and all suggestions. Thank you in advance.