SED replace few first occurences ( and ranges ) of pattern - sed

Question

is this possible to change first 4 ( or more ) occurences of string in this scenario using SED (opposite of sed -r 's/[^[:space:]]*/TEST/4g'):
TEST TEST TEST TEST five six seven
I get it working with reversing words order in line using AWK twice, but this is long, complex and I want to get this with just SED:
echo one two three four five six seven | awk '{for(i=NF;i>=1;i--) printf "%s ", $i;print ""}' | sed -r 's/[^ ]*/TEST/4g' | awk '{for(i=NF;i>=1;i--) printf "%s ", $i;print ""}'
Also maybe there is option to change ranges of occurence like 3-5, 6-12, ...?
Example input is:
one two three four five six seven
eight nine ten eleven twelve thirteen fourteen
fifteen sixteen seventeen eighteen nineteen twenty twenty-one

Answer 1

What about a single AWK:
awk '{for(i=1;i<=NF;i++) if(i<5){$i="TEST"}; print}'
Test run:
$ echo one two three four five six seven | awk '{for(i=1;i<=NF;i++) if(i<5){$i="TEST"}; print}'
TEST TEST TEST TEST five six seven
This solution is short, readable and maintainable. If it does not satisfy you, please add some details about your specific problem.
Perl equivalent solution:
perl -pe 's/\S+/$i++<4?"TEST":$&/ge'
Test run:
$ echo one two three four five six seven | perl -pe 's/\S+/$i++<4?"TEST":$&/ge'
TEST TEST TEST TEST five six seven
maybe there is option to change ranges of occurence like 3-5, 6-12
AWK:
awk '{for(i=3;i<6;i++)$i="TEST";print}'
Test run on the newly provided input file:
$ awk '{for(i=3;i<6;i++)$i="TEST";print}' input
one two TEST TEST TEST six seven
eight nine TEST TEST TEST thirteen fourteen
fifteen sixteen TEST TEST TEST twenty twenty-one
Perl:
perl -pe 's/\S+/++$c~~[3..5]?"TEST":$&/ge'
Test run on the newly provided input file:
$ perl -pe '$c=0;s/\S+/++$c~~[3..5]?"TEST":$&/ge' input
Smartmatch is experimental at -e line 1. <== This is a warning that goes to STDERR
one two TEST TEST TEST six seven
eight nine TEST TEST TEST thirteen fourteen
fifteen sixteen TEST TEST TEST twenty twenty-one

Answer 2

The answer has been provided here by mikeserv. NOTE: if you want to process a range, you need to use the maximum bound, as it will process as many matches as it can without throwing any exceptions/errors.
GNU sed:
echo 'one two three four five six seven' | \
sed 's/[^[:space:]]*/\n&/g;:t;/\n/{x;/.\{4\}/!{s/$/./;x;s/\n[^[:space:]]*/TEST/;bt};x};s/\n//g'
POSIX sed:
nl='
';
echo 'one two three four five six seven' | sed "s/[^[:space:]]*/\\$nl&/g;:t${nl}/\n/{x;/.\{4\}/!{${nl}s/$/./;x;s/\n[^[:space:]]*/TEST/;bt$nl};x$nl};s/\n//g"
See the online sed demo.
Original explanation (note that here, 1 is replaced with 2, you may use any other patterns):
There I use two notable techniques. In the first place every
occurrence of 1 on a line is replaced with \n1. In this way, as I
do the recursive replacements next, I can be sure not to replace the
occurrence twice if my replacement string contains my replace
string. For example, if I replace he with hey it will still work.
I do this like:
s/1/\
&/g
Secondly, I am counting the replacements by adding a character to
hold space for each occurrence. Once I reach three no more occur. If
you apply this to your data and change the \{3\} to the total
replacements you desire and the /\n1/ addresses to whatever you mean
to replace, you should replace only as many as you wish.

Answer 3

This is a completely inappropriate task for sed as sed is for doing simple s/old/new/ on individual strings, that is all. With any awk in any shell on every UNIX box:
$ echo one two three four five six seven | awk '{for (i=1; i<=4; i++) $i="TEST"}1'
TEST TEST TEST TEST five six seven
$ echo one two three four five six seven | awk '{for (i=3; i<=5; i++) $i="TEST"}1'
one two TEST TEST TEST six seven
and if you need to parameterize it:
echo one two three four five six seven |
awk -v beg=3 -v end=5 '{for (i=beg; i<=end; i++) $i="TEST"}1'
one two TEST TEST TEST six seven

Answer 4

$ echo "one two three four fix six" | \
sed -E ':r s/(^|(TEST )+)[^ ]*/\1TEST/;/^(TEST ){4}/!br'
TEST TEST TEST TEST fix six
Explanation:
:r label named r to branch back to
s/(^|(TEST )+)[^ ]*/\1TEST/; replacement that replaces just one occurrence of a non-TEST word, preceeded by either the start of the line or 1 or more TESTs
/^(TEST ){4}/!br' regex for what's wanted, followed by the !br to branch back to :r if it's not matched yet.
Clearly this is fragile. It will loop infinitely if any lines don't have four words. Might be GNU sed only.