Existem muitas maneiras de fazer isso. Você pode ler o arquivo e remover o espaço em todas as linhas depois de cujo segundo campo for maior que 9999:
$ awk '$2>9999{sub(/ /,"")}1;' file
ATOM 9996 CG GLU 622 -13.525 -7.714 -11.215 0.0136 1.9080 0.1094
ATOM 9997 2HG GLU 622 -12.773 -7.608 -11.999 -0.0425 1.4870 0.0157
ATOM 9998 3HG GLU 622 -13.121 -8.370 -10.441 -0.0425 1.4870 0.0157
ATOM 9999 CD GLU 622 -14.803 -8.348 -11.783 0.8054 1.9080 0.0860
ATOM 10000 OE1 GLU 622 -15.541 -9.019 -11.024 -0.8188 1.6612 0.2100
ATOM 10001 OE2 GLU 622 -15.105 -8.223 -12.988 -0.8188 1.6612 0.2100
ATOM 10002 C GLU 622 -13.072 -4.215 -9.499 0.5366 1.9080 0.0860
ATOM 10003 O GLU 622 -13.537 -3.437 -10.330 -0.5819 1.6612 0.2100
ATOM 10004 N TYR 623 -12.988 -3.858 -8.210 -0.4157 1.8240 0.1700
ATOM 10005 H TYR 623 -12.684 -4.551 -7.536 0.2719 0.6000 0.0157
ATOM 10006 CA TYR 623 -13.410 -2.540 -7.700 -0.0014 1.9080 0.1094
ATOM 10007 HA TYR 623 -13.794 -1.927 -8.513 0.0876 1.3870 0.0157
ATOM 10008 CB TYR 623 -14.530 -2.720 -6.667 -0.0152 1.9080 0.1094
ATOM 10009 2HB TYR 623 -14.107 -3.312 -5.863 0.0295 1.4870 0.0157
ATOM 10010 3HB TYR 623 -14.784 -1.738 -6.265 0.0295 1.4870 0.0157
ATOM 10011 CG TYR 623 -15.831 -3.390 -7.081 -0.0011 1.9080 0.0860
ATOM 10012 CD1 TYR 623 -16.301 -3.357 -8.410 -0.1906 1.9080 0.0860
Como alternativa, você pode alinhar tudo:
$ perl -lane 'printf "%-5s%6s %-3s%4s%5d%8s%8s%8s%8s%8s\n",@F' file
ATOM 9996 CG GLU 622 -13.525 -7.714 -11.215 0.0136 1.9080
ATOM 9997 2HG GLU 622 -12.773 -7.608 -11.999 -0.0425 1.4870
ATOM 9998 3HG GLU 622 -13.121 -8.370 -10.441 -0.0425 1.4870
ATOM 9999 CD GLU 622 -14.803 -8.348 -11.783 0.8054 1.9080
ATOM 10000 OE1 GLU 622 -15.541 -9.019 -11.024 -0.8188 1.6612
ATOM 10001 OE2 GLU 622 -15.105 -8.223 -12.988 -0.8188 1.6612
ATOM 10002 C GLU 622 -13.072 -4.215 -9.499 0.5366 1.9080
ATOM 10003 O GLU 622 -13.537 -3.437 -10.330 -0.5819 1.6612
ATOM 10004 N TYR 623 -12.988 -3.858 -8.210 -0.4157 1.8240
ATOM 10005 H TYR 623 -12.684 -4.551 -7.536 0.2719 0.6000
ATOM 10006 CA TYR 623 -13.410 -2.540 -7.700 -0.0014 1.9080
ATOM 10007 HA TYR 623 -13.794 -1.927 -8.513 0.0876 1.3870
ATOM 10008 CB TYR 623 -14.530 -2.720 -6.667 -0.0152 1.9080
ATOM 10009 2HB TYR 623 -14.107 -3.312 -5.863 0.0295 1.4870
ATOM 10010 3HB TYR 623 -14.784 -1.738 -6.265 0.0295 1.4870
ATOM 10011 CG TYR 623 -15.831 -3.390 -7.081 -0.0011 1.9080
ATOM 10012 CD1 TYR 623 -16.301 -3.357 -8.410 -0.1906 1.9080