datastore - Writing data to a text file without erasing old data after Quit Kernel?

The example code is as following:

currentdirectory = NotebookDirectory[];
SetDirectory[currentdirectory];
datapath = FileNameJoin[{currentdirectory, "store.txt"}];

Steps = 3; 

For[ii = 1, ii <= Steps, ii++,
 testlist = {1, 2, 0, 0};
 WriteLine[datapath, testlist];
 ]

When I Quit Kernel or Close the code and Run it again, I cannot continue writing data to the exist text file. The store.txt is always rewritten instead of being continuing data writing.

The solution I do is that I first load the store.txt and rewrite it again , then I continue to write data to store.txt, the code is the following:

currentdirectory = NotebookDirectory[];
SetDirectory[currentdirectory];

datapath = FileNameJoin[{currentdirectory, "store.txt"}];

If[FileExistsQ[datapath] == True,
   storelist = Import["store.txt"];
   WriteLine[datapath, storelist];
  ];

Steps = 3; 
For[ii = 1, ii <= Steps, ii++,
  testlist = {1, 2, 0, 0};

  WriteLine[datapath, testlist];
  ];

From the store.txt file, we can see the data is continuing written in the text file.

In the above example, I use Steps=3. Actually it will be a large number such as 10000 or even large. So I think my solution is not efficient.

I wonder whether there is any way to make it quick or that I don't need to load the data and rewrite first. Thank you very much!

Updates: @enano9314 suggests using OpenAppend which I wrote is as following:

currentdirectory = NotebookDirectory[];
SetDirectory[currentdirectory];

datapath = FileNameJoin[{currentdirectory, "store.txt"}];
If[FileExistsQ[datapath] == True,
  flag = 0;
  str = OpenAppend[File[datapath]],
  flag = 1;
  str = datapath;
  ];

Steps = 3; 
For[ii = 1, ii <= Steps, ii++,

  testlist = {1, 1, 1, 1};
  WriteLine[str, testlist];
  ];
If[flag = 0;
  Close[str],
  Close[File[str]];
  ];