Non modifiable procedures are called

Serially usable procedures

Serially usable procedures are a set of procedures that can be performed in a specific order to achieve a desired result.
These procedures are typically clear and concise, and they are designed to be easily followed by individuals or groups.
Some examples of serially usable procedures may include instructions for assembling a piece of furniture, performing a series of experiments in a lab, or completing a complex task in a manufacturing setting. These procedures are often written down or documented in some way, such as in a manual or on a website, to ensure that they are easy to access and understand by those who need to use them.

Concurrent procedures refer to the execution of multiple tasks or processes at the same time.
This can be achieved through the use of multitasking systems or through the use of parallel processing techniques. Concurrent procedures are often used in computer systems to increase efficiency and speed up the completion of tasks.
They can also be used in other fields, such as healthcare or manufacturing, to allow multiple tasks to be completed simultaneously.

Reentrant procedures are procedures that can be interrupted and then resumed at a later point in time, without causing any errors or inconsistencies in the program.
They are designed to allow multiple threads or processes to access the same procedure simultaneously, without causing conflicts or deadlocks.
Reentrant procedures are often used in multi-threaded or concurrent programming environments, where multiple threads or processes may need to access shared resources or data structures concurrently.

Non modifiable procedures are called Reentrant procedures