If you have the EX4 and understand what the bot does, you can hire a developer on the official MQL5 forum to rewrite the logic from scratch in a new MQ4 file.
If you only need to change a small parameter (like a hardcoded expiration date), a Hex Editor might be more effective than a full decompiler. ex4 decompiler github
(by anonymoux007 )
When you compile an MQ4 file inside the MetaEditor IDE, the platform translates your readable code into low-level p-code (pseudo-code) stored in the EX4. —replacing them with memory addresses and stack operations. Ex4 Decompiler on GitHub: Overview & Key Tools