Or without explicit capturing or evaluation (or rounding!) (update: and with dynamic control of truncation threshold), but needs Perl version 5.10+ for  \K operator:

c:\@Work\Perl\monks>perl -wMstrict -le
"use 5.010;
 ;;
 my $content
   = qq/{ \"geometry\": { \"type\": \"Polygon\", \"coordinates\": [ [ 
+[ 19.05480
4912278406, \n/
   . qq/47.485785556135411 ], [ 19.057857836771483, 47.487322542030711
+ ], [ 19.06025597925397, \n/
   . qq/47.488491565765209 ], [ 19.060347248086835, 47.488539642204628
+ ], [ 19.060463310421543, \n/
   . qq/47.484578287406251 ], [ 19.054804912278406, 47.485785556135411
+ ] ] ] } } \n/
   ;
 print qq{[[$content]]};
 ;;
 my $n = 7;
 $content =~ s{ \d [.] \d{$n} \K \d+ }{}xmsg;
 ;;
 print qq{<<$content>>};
"
[[{ "geometry": { "type": "Polygon", "coordinates": [ [ [ 19.054804912
+278406,
47.485785556135411 ], [ 19.057857836771483, 47.487322542030711 ], [ 19
+.06025597925397,
47.488491565765209 ], [ 19.060347248086835, 47.488539642204628 ], [ 19
+.060463310421543,
47.484578287406251 ], [ 19.054804912278406, 47.485785556135411 ] ] ] }
+ }
]]
<<{ "geometry": { "type": "Polygon", "coordinates": [ [ [ 19.0548049,
47.4857855 ], [ 19.0578578, 47.4873225 ], [ 19.0602559,
47.4884915 ], [ 19.0603472, 47.4885396 ], [ 19.0604633,
47.4845782 ], [ 19.0548049, 47.4857855 ] ] ] } }
>>
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