Simply assign it to another variable.
global evil_global_var;
saved_evil_global_val = evil_global_var;
evil_global_var = new_val;
... % do your stuff here
evil_global_var = saved_evil_global_val; % retore your global value here
Now, most globals are unncessary and can be replaced be well-defined functions with input arguments.
Blessings,
Spencer
