msbar changes a sequence a lot or a little, attempting to emulate various forms of mutation. You can set the number and types of mutations.

Here is a sample session with msbar. This asks for 5 mutations, with point mutations as changes (substitutions) and the codon and block mutations ignored:

% msbar
Input sequence: embl:eclaci
Output sequence [eclaci.fasta]: 
Number of times to perform the mutation operations [1]: 5
Point mutation operations
         0 : None
         1 : Any of the following
         2 : Insertions
         3 : Deletions
         4 : Changes
         5 : Duplications
         6 : Moves
Types of point mutations to perform [0]: 4
Codon mutation operations
         0 : None
         1 : Any of the following
         2 : Insertions
         3 : Deletions
         4 : Changes
         5 : Duplications
         6 : Moves
Types of codon mutations to perform [0]:
Block mutation operations
         0 : None
         1 : Any of the following
         2 : Insertions
         3 : Deletions
         4 : Changes
         5 : Duplications
         6 : Moves
Types of block mutations to perform [0]:

Mandatory qualifiers (bold if not always prompted):

[-sequence] (seqall)

Sequence database USA.

-count (integer)

Number of times to perform the mutation operations.

-point (menu)

Types of point mutations to perform.

-block (menu)

Types of block mutations to perform.

-codon (menu)

Types of codon mutations to perform. These are only done if the sequence is nucleic.

[-outseq] (seqoutall)

Output sequence(s) USA.

Optional qualifiers (bold if not always prompted):

-inframe (boolean)

Do codon and block operations in frame.

Advanced qualifiers:

-minimum (integer)

Minimum size for a block mutation.

-maximum (integer)

Maximum size for a block mutation.