$entry_array[ 'entry' ][0] .= 'TEST';
echo $entry_array[ 'entry' ][0];// to see its NEW contents

Gives - Fatal error: Cannot use assign-op operators with overloaded objects nor string offsets

Then i go to alternative so - $entry_array[ 'entry' ][0] = $entry_array[ 'entry' ][0] . 'TEST';
echo $entry_array[ 'entry' ][0];// to see its NEW contents

Gives - <<<<<
<<<<<
<<<<<
<<<<<
<<<<<
<<<<<
<<<<<
<<<<<
<<<<<
<<<<<

and all the entries below...