Overview
One thing I have noticed about 'Everyone's a Wally' is that it's data structures were ahead of a lot of other games released at that time. The data is very well organised, it is of variable length, which can save a hell of a lot of memory and uses some clever command codes to help keep the data length down.
If you are thinking of changing the data in Wally, you must keep in mind my comment about it being of variable length. This means you can't just change one thing without altering the length of the whole data string. Which in turn moves all of the other parts of the data. Additionally, Mikro-Gen have used tables, of pointers, in ordr to index the start of each data structure, so any alterations require these to be changed to match. Since 'wally' isn't the sort of program you can change lightly, such as Jetset Willy, you really need to plan all of your changes first.
Note that all of the addresses and values are in hex, you can use the desktop calculators that come with most OS's to translate these to decimal should you wish, but it is always easier to work in hex when dealing with assembly and data.