Perhaps this will get you part of the way to where you want to go
In[1]:= 2380570.51
Out[1]= 2.38057*10^6
In[2]:= $PrePrint = AccountingForm[#, NumberSigns->{"-",""}]&;
In[3]:= 2380570.51
Out[3]= 2380571.
In[4]:= 10^21
Out[4]= 1000000000000000000000
That removes the scientific notation on output, but does not deal with the issue of how many digits should be displayed when the number includes a decimal point because that is a much more involved subject.
You can turn this back off with this
In[5]:= $PrePrint =.
In[6]:= 2380570.51
Out[6]= 2.38057*10^6
Please be careful with this. Any time you get close to violating one of the fundamental principles of an organized body of knowledge you then run the risk of unexpected consequences.