Actually, 32 bytes

0'u';"7╙D@%c◙0"'#,⌠";#"íu⌡░ΣÆƃX 

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##Explanation

This Actually program converts the ;# program to an Actually program through simple string substitution. With the accumulator value on top of the stack, the ;# ; instruction is equivalent to u in Actually (increment), and # is equivalent to 7╙D@%c◙0 (modulo by 2**7-1, convert to ASCII char, print without newline, push 0).

0'u';"7╙D@%c◙0"'#,⌠";#"íu⌡░ΣÆƃX 0  push 0 (the initial accumulator value)   ,⌠";#"íu⌡░  filter (take only values where function returns truthy):   ";#"íu one-based index of the character in the string ";#", or 0 if not found Σ  concatenate   "7╙D@%c◙0"'#  Æ  replace "#" with "7╙D@%c◙0" in the input  'u';  Æ  replace ";" with "u"   ƒ execute the code   X discard the accumulator value 

Actually, 20 bytes

'#@s⌠';@c7╙D@%c⌡MdXΣ 

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Explanation:

'#@s⌠';@c7╙D@%c⌡MdXΣ '#@s split on "#" ⌠';@c7╙D@%c⌡M for each chunk: ';@c count occurrences of ";" 7╙D@% mod by 127 (2**7-1) c convert to ASCII char dX discard last item Σ concatenate 

Actually, 35 bytes

0'u';"7╙D@%c◙0"'#,⌠;";#"íub*⌡MΣÆƃX 

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##Explanation

This Actually program converts the ;# program to an Actually program through simple string substitution. With the accumulator value on top of the stack, the ;# ; instruction is equivalent to u in Actually (increment), and # is equivalent to 7╙D@%c◙0 (modulo by 2**7-1, convert to ASCII char, print without newline, push 0).

0'u';"7╙D@%c◙0"'#,⌠;";#"íub*⌡MΣÆƃX 0  push 0 (the initial accumulator value) ,⌠;";#"íub*⌡MΣ  peform the following on each character in the input and concatenat the result: ; duplicate the character   ";#"íu  one-based index of the character in the string ";#", or 0 if not found   b*  convert to boolean and repeat the character that many times (1 if it is ";" or "#" and 0 otherwise) "7╙D@%c◙0"'#  Æ replace "#" with "7╙D@%c◙0" in the input 'u';  Æ replace ";" with "u"   ƒ execute the code   X discard the accumulator value 

Actually, 32 bytes

0'u';"7╙D@%c◙0"'#,⌠";#"íu⌡░ΣÆƃX 

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##Explanation

This Actually program converts the ;# program to an Actually program through simple string substitution. With the accumulator value on top of the stack, the ;# ; instruction is equivalent to u in Actually (increment), and # is equivalent to 7╙D@%c◙0 (modulo by 2**7-1, convert to ASCII char, print without newline, push 0).

0'u';"7╙D@%c◙0"'#,⌠";#"íu⌡░ΣÆƃX 0 push 0 (the initial accumulator value) ,⌠";#"íu⌡░ filter (take only values where function returns truthy): ";#"íu one-based index of the character in the string ";#", or 0 if not found Σ concatenate "7╙D@%c◙0"'# Æ replace "#" with "7╙D@%c◙0" in the input 'u'; Æ replace ";" with "u" ƒ execute the code X discard the accumulator value 

Actually, 17 bytes

'#@s♂l7╙D@♀%♂cdXΣ 

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Explanation:

'#@s♂l7╙D@♀%♂cdXΣ '#@s split input on "#" ♂l length of each chunk of semicolons 7╙D@♀% modulo each length with 127 (2**8-1) ♂c convert to ASCII character dX discard the last one Σ concatenate 

Actually, 35 bytes

0'u';"7╙D@%c◙0"'#,⌠;";#"íub*⌡MΣÆƃX 

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##Explanation

This Actually program converts the ;# program to an Actually program through simple string substitution. With the accumulator value on top of the stack, the ;# ; instruction is equivalent to u in Actually (increment), and # is equivalent to 7╙D@%c◙0 (modulo by 2**7-1, convert to ASCII char, print without newline, push 0).

0'u';"7╙D@%c◙0"'#,⌠;";#"íub*⌡MΣÆƃX 0  push 0 (the initial accumulator value) ,⌠;";#"íub*⌡MΣ  peform the following on each character in the input and concatenat the result:  ; duplicate the character ";#"íu one-based index of the character in the string ";#", or 0 if not found   b*  convert to boolean and repeat the character that many times (1 if it is ";" or "#" and 0 otherwise)   "7╙D@%c◙0"'#  Æ replace "#" with "7╙D@%c◙0" in the input  'u'; Æ replace ";" with "u"  ƒ execute the code X discard the accumulator value