Permission for users

Hello everybody!
I got several access groups, each divided by our unit in Brazil.
A group of salespeople, managers, financial and etc…
However, let me make 02 fields of PurchTable and SalesTable only editable for some users.
How many groups have access (about 160), would like to edit the form itself access to these fields (SalesLine.TaxItemGroup, SalesLine.Taxgroup / PurchLine.TaxItemGroup, PurchLine.Taxgroup).
I created a task to not allow printing / exporting in another form, but do not know whether to editing fields is possible.
Under the task that I use to allow only certain users have full access on the form.
Can I get something similar?

Hugs,

public int task(int _taskId)

{

UserId currentUserId = curUserId();

int ret;

#task

;

if(_taskId == 4436 || _taskId == 2832 || _taskId == 770 || _taskId == 771 || _taskId == 772 || _taskId == 278)

{

if(currentUserId == “Admin” || currentUserId == “mateu” || currentUserId ==“joao1” || currentUserId ==“fra11”)

{

ret = super(_taskId);

}

}

else

ret = super(_taskId);

return ret;

}