Assimilation of phones

Change in place of articulation caused by trailing phone

NG

a) <ng> the phone represented by the <n> is different from [n].

b) <ng> = [ng] German: Bahngleis

In German both a+b exist. Other Germanic languages may have that too. So, the writing is not phonetic.

Change in voicing caused by preceding phone

TQ

Polish <rz> is voiced, preceded by <t> it is voiceless

Change in plosive release ?

TC?

a) <tc> = [t︠ʃ︡] - I think one could say the [t] is changed, or the start of the [ʃ]. But at the end there is [ʃ]. https://www.internationalphoneticassociation.org/sites/default/files/IPA_Kiel_2015.pdf

[t] = column (place?): alveolar; row (manner?): plosive
[ʃ] = column: postalveolar; row: fricative
[t︠ʃ︡] = not present, but it says "affricates can be represented by two symbols if joined by a tie bar if necessary" - the if-clause could refer to the tie bar.

https://en.wikipedia.org/wiki/Template:IPA_consonant_chart has it without tie bar column: palato-alveolar; row: sibilant affricate

The result has the column of the second. The row is new. Voicing for all is unvoiced.

That is different from Polish <cz> where

<c> = [t͡s] = column: alveolar; row: is a sibilant affricate; voicing: unvoiced
<z> = [z] = column: alveolar; row: fricative/sibilant fricative; voicing: voiced

Comparing with the result: <cz> = [t︠ʃ︡] : The resulting column is not involved for the source symbols (different from <tc>). The row is different (like for <tc>). The voicing is different for one of the phones represented by the source symbols (different from <tc>).

If <tc> = [t︠ʃ︡]

b) <tc> = [tʃ] - no change