How to continuously manipulate other website data?

I have used JS injector extensions on chrome to manipulate data on other website ( to see things in the way I want it to be ) but this method doesn't work on websites where the data is continuously changing.

For example, lets say I open Yahoo Finance where stock data is displayed live. I want to manipulate that data, meaning whatever live data is being displayed I want to multiply 100 to them and see that happening live and continuously. Is there any way to apply JS injection ( onchange ) kind of function to detect change and multiply 100x right away.